r\UL     s*.jji  ».c  a»v     /r^>  ^^ma,  /aR,1, 


University  of  Illinois 


Library  at 
Urbana-Champaign 


UNIVERSITY  LIBRARY 

UNIVERSITY  OF  ILLINOIS  AT  URBANA-CHAMPAIGN 

The  person  charging  this  material  is  responsible  for  its 


renewal  or  return  to  the  library  on  or  before  the  due      $J|f 'J^JS 

date.  The  minimum  fee  for  a  lost  item  is  $125.00, 

$300.00  for  bound  journals. 

Theft,  mutilation,  and  underlining  of  books  are  reasons 

for  disciplinary  action  and  may  result  in  dismissal  from 

the  University.  Please  note:  self-stick  notes  may  result 

in  torn  pages  and  lift  some  inks. 

Renew  via  the  Telephone  Center  at  217-333-8400, 

846-262-1510  (toll-free)  orcirclib@uiuc.edu. 

Renew  online  by  choosing  the  My  Account  option  at: 

http://www.library.uiuc.edu/catalog/ 


"JVuV 

$&|p 
<9» 


UNIVERSITY  OF  ILLINOIS 


Agricultural  Experiment  Station 


BULLETIN  No.  118 


BITTER  ROT  OF  APPLES 
Botanical  Investigations 


BY  THOMAS  J,  BURRILL 


URBANA,  ILLINOIS,   SEPTEMBER,  1907 


SUMMARY  OF  BULLETIN  No.   118 

Bitter  rot  of  apples,  an  exceedingly  destructive  disease  attack- 
ing fruit  on  the  tree,  is  due  to  a  specific  fungus  called  Glonierella 
rufomaculans,  which  though  sometimes  found  on  other  fruits,  and 
which  can  be  artificially  grown  upon  many  substances,  is  in  Illinois 
practically  confined  to  apples  and  to  apple-tree  limbs.  On  the  lat- 
ter the  affected  spots  are  called  cankers.  There  are  two  forms  of 
spores,  but  they  appear  to  be  alike  in  function,  neither  of  them 
being  specialized  to  survive  the  winter.  It  is  the  mycelium  in  the 
cankers  and  in  old  infected  fruits  that  does  this.  Page  555 

Limbs  of  apple  trees  become  infected  only  in  spots  where  the 
bark  has  been  previously  injured  mechanically  or  by  some  other 
parasite.  Cankers  may  originate  as  late  as  the  time  of  the  apple 
harvest  and  in  wounds  made  at  this  time.  Page  561 

The  spores  are  very  easily  destroyed  by  copper  sulphate.  It 
seems  impossible  to  kill  the  fungus  in  the  limb  cankers  by  any  per- 
missible external  application.  They  must  be  destroyed  by  cutting 
off  the  affected  limbs.  Page  563 

Outbreaks  of  the  disease  usually  begin  in  July  or  August,  but 
may  start  as  early  as  June  I,  in  north  latitude  38°.  Page  571 

The  spores  are  to  some  extent  distributed  by  pomace  flies, 
but  no  insects  are  largely  instrumental  in  the  distribution  or  devel- 
opment of  the  disease.  The  spores  are  readily  washed  from  can- 
kers and  infected  fruits  to  fresh  fruits  hanging  below  in  the  tree. 
Light  showers  most  effectively  aid  infection.  Spores  and  spore- 
masses  are  distributed  by  wind,  sometimes  to  considerable  dis- 
tances. Page  572 

New  apples  are  first  infected  only  by  spores  produced  in  limb 
cankers  or  in  infected  apples  (mummies)  of  the  previous  year 
which  have  hung  during  the  winter  on  the  trees.  Neither  the 
fungus  nor  its  spores  live  over  winter  in  the  grounder  in  anything 
upon  the  ground.  Page  580 

The  absolute  eradication  of  the  disease  from  an  orchard  is  en- 
tirely possible  by  careful  collection  and  destruction  of  the  cankers 
and  mummies,  faithfully  supplemented  by  effective  spraying  with 
Bordeaux  mixture  and  the  prompt  removal  of  early  infected  fruit. 

Page  593 

Bulletin  No.  117  should  be  consulted  for  methods  and  results 
of  spraying.  * 


BITTER  ROT  OF  APPLES 
Botanical  Investigations 

BY  THOMAS  J.  BURRILL,  CHIEF  IN  BOTANY 
INTRODUCTION 

The  fungus  to  which  the  decidedly  distinctive  disease  of  apple 
fruits  called  bitter  rot  is  due,  is  undoubtedly  of  American  origin 
and  the  disease  seems  to  be  still  confined  to  our  own  country.  With 
us  its  geographical  extension  is  very  wide,  but  offers  peculiarities 
of  development  which  are  apparently  due  solely  to  climatic  charac- 
teristics. It  attacks  apples  on  the  tree  during  any  period  of  the  sea- 
son when  hot,  humid  weather  prevails,  and  is  at  its  worst  enor- 
mously destructive, — an  estimate  of  $10,000,000  a  year  for  the 
United  States  cannot  be  considered  an  exaggeration. 

The  disease  has  long  been  recognized  but  where  it  came  from  or 
to  what  cause  it  could  be  attributed  was  little  understood.  Since  it 
frequently  occurred  year  after  year  upon  some  particular  tree  or 
trees  it  was  supposed  to  result  from  something  inherent,  some  inside 
characteristic  of  the  tree  itself,  or  that  the  poison  rose  in  the  sap 
from  some  source  not  explained.  An  outbreak  often  seemed  ex- 
ceedingly sudden,  and  as  the  origin  was  mysterious,  prevention  or 
cure  was  entirely  beyond  reach.  There  was  nothing  to  do  but  help- 
lessly to  submit  to  the  inevitable.  The  promise  of  a  fine  harvest, 
perhaps  after  the  fruit  was  nearly  or  fully  grown,  was  swept  away 
as  by  the  breath  of  contagion,  blasting  in  a  few  days  the  apparently 
well-founded  hopes  of  the  orchardist  for  requisite  remuneration  for 
his  year's  labor  and  expenditures.  There  was  something  in  it  ap- 
parently beyond  recognition, — something  mysterious,  something 
outside  of  the  run  of  ordinary  cause  and  effect.  While  apples  were 
grown  principally  for  home  use,  the  losses,  though  keenly  felt,  were 
not  counted  in  dollars  and  cents;  but  as  orchards  were  increased  in 
size  and  apple-growing  assumed  commercial  importance  the  inroads 
made  seemed  still  harder  to  bear  and  came  to  be  reckoned  in  finan- 
cial terms,  rising  sometimes  even  in  the  case  of  single  plantations 
into  the  thousands. 

It  was  at  this  stage  that  the  matter  began  to  receive  serious  at- 
tention on  the  part  of  the  state  agricultural  experiment  stations 
most  directly  concerned,  and  by  the  pathologists  of  the  United  States 

555 


556  BULLETIN  No.  118.  [September, 

Department  of  Agriculture.  Some  direct,  successful  studies  were 
made  during  the  last  quarter  of  the  Nineteenth  Century,  and  certain 
other  important  discoveries  found  afterward  helpful  had  been  made, 
but  the  knowledge  which  is  at  this  date  relied  upon  as  a  guide  in 
the  prevention  of  these  losses  has  mainly  resulted  from  investiga- 
tions undertaken  since  the  beginning  of  the  year  1900.  Thanks  to 
these  studies  and  experiments,  it  may  now  be  said  that  what  for- 
merly seemed  incomprehensible  is  easily  understandable.  The  cause 
of  the  difficulty  has  been  ascertained  and  a  fungus  identified  as  that 
cause.  The  time  has  gone  by  for  any  one  to  cavil  in  regard  to  the 
application  of  the  word  "cause"  so  used.  It  is  true  that  the  parasite 
must  have  conditions  suited  to  itself,  but  conditions  are  not  active 
agents.  It  is  the  fungus  as  the  active  agent  working  under  permis- 
sible conditions  of  susceptible  fruits  and  of  heat  and  moisture  which 
must  be  charged,  if  there  is  to  be  such  a  charge,  with  the  cause  of 
the  effects  witnessed.  Combative  measures  to  be  direct  must  be 
upon  this  basis,  and  even  the  control  of  conditions  must  be  upon  the 
assumption  that  this  means  warfare  upon  the  living,  in  jury- working 
parasite. 

Fortunately  there  is  no  longer  reason  to  fear  great  losses  from 
this  infectious  disease.  No  one  need  permit  the  destruction  of  a 
crop  of  well-grown  fruit.  The  destroyer  has  not  only  been  iden- 
tified and  its  mode  of  life  made  known,  but  means  of  successful 
combat  have  been  ascertained.  It  is  hoped  this  bulletin  and  the  com- 
panion one  from  the  department  of  horticulture  will  be  found  to  be 
useful  additions  to  former  luminous  literature  upon  the  subject. 
While  in  this  number  studies  upon  the  fungus  are  reported,  in  Bul- 
letin 1 17,  by  Professor  Joseph  C.  Blair,  the  mean's  of  control  are 
clearly  and  conclusively  set  forth.  Perhaps  never  before  in  the 
history  of  any  parasitic  plant  disease  has  there  been  such  elaborate 
experimentation  under  circumstances  and  methods  so  likely  to  fur- 
nish incontestable  results. 

Besides  the  acknowledgments  given  in  the  text  it  should  be  said 
Mr.  James  T.  Barrett,  First  Assistant  in  Botany,  has  had  a  very 
large  part  in  these  investigations  since  1903.  _  He  has  efficiently  Car- 
ried into  execution  the  plans  for  the  various  experiments  reported  and 
has  more  or  less  devised  his  own  methods  of  procedure.  The  lab- 
oratory and  field  notes  appended  under  the  different  subjects  are 
substantially  as  written  out  by  him.  The  illustrations  were  all  made 
by  him  except  as  otherwise  credited. 

For  a  general  citation  of  literature  see  Von  Schrenk,  Hermann  and  Spaulding-,  Perley 
The  Bitter  Rot  of  Apples,  Bui.  TJ.  S.  Dept.  Apr.,  Bui.  Pit.  Ind.44:  46-51,  1903. 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  557 

PART  I     GENERAL  INFORMATION 

The  so-called  bitter  rot  of  apples  owes  its  name  to  the  taste  of 
the  affected  tissue,  but  this  varies  much  from  an  exceedingly  bitter 
quality  to  that  which  can  scarcely  be  so  identified.  The  term  ripe 
rot  sometimes  applied  is  much  more  of  a  misnomer  for  the  disease 
is  especially  one  of  growing  fruits. 

The  malady  is  easily  recognized  by  the  very  characteristic,  black, 
circular,  sharply  margined  spots  on  fruits  varying  in  size  from  an 
eighth  to  three- fourths  or  more  of  an  inch  in  diameter  (PI.  III., 
Fig.  2. )  These  spots  become  somewhat  depressed  by  the  shrinkage 
of  the  affected  tissues  which  are  always  dry  and  become  leathery 
and  even  corky  in  texture.  Properly  then  the  effect  is  not  that  of  a 
rot  at  all.  On  the  contrary  the  pulpy  substance  of  apples  is  well 
preserved  from  ordinary  decay  through  the  action  of  this  infecting 
agent. 

The  disease  occurs  practically  throughout  the  United  States, 
wherever  apples  are  very  much  grown,  from  Maine  to  Texas  and 
from  Michigan  to  Louisiana,  but  is  greatly  more  injurious  in  cer- 
tain large  areas,  the  largest  of  which  seems  to  be  a  broad  belt  ex- 
tending from  Virginia  to  Oklahoma,  roughly  between  the  parallels 
of  35  and  39  degrees  of  north  latitude.  In  Illinois  it  has  not  been 
seriously  troublesome  north  of  some  30  to  40  miles  south  of  Spring- 
field. Further  southward  it  has  often  destroyed  a  million  or  more 
dollars  worth  of  fruit  a  year. 

It  is  well  known  that  the  destructive  disease  of  apples  just  de- 
scribed is  due  to  a  specific  fungus,  which  was  long  called  Glccospor- 
ium  fructigenum  Berk.,  but  which  has  more  recently  been  referred 
to  as  Glomerella rufomaculans  (Berk.)  Spauld.  and  Von  Schrenk.1 
This  fungus  grows  on  developing  apples,  beginning  at  any  time  dur- 
ing the  summer  or  autumn  when  the  conditions  are  favorable  after 
the  fruits  are  formed  and  until  and  after  they  are  ripe;  and  it  lives 
as  a  parasite  in  the  bark  of  apple-tree  limbs,  usually  in  localized 
areas  called  cankers.  It  does  not  occur  upon  the  leaves. 

The  same  fungus  grows  in  the  same  way  upon  several  other 
fruits';  such  as  pears,  quinces,  peaches,  and  grapes,  and  even  on 
tomatoes,  pepers,  egg-plants,  etc.  (PI.  III.  Fig.  i.)  Sometimes 
it  naturally  develops  on  grape  berries  to  a  destructive  extent; 
but  commonly  it  is  only  decidedly  injurious  to  apples,  and  has  never 
been  reported  as  formine  limb-cankers  on  other  trees.  It  seems, 
however,  to  develop  as  a  parasite  in  some  cases  on  the  stems  of 

1.  The  fungus  referred  to  in  this  bulletin  is  the  same  as  that  for  which  this  name  was  pro- 
ed,  whatever  may  be  said  of  the'name  itself,  a  matter  not  here  given  further  consideration. 


pose 


558  BULLETIN  No.  118.  [September, 

sweet  peas,1  and  what  is  probably  the  same  fungus  causes  the  so- 
called  "mummy"  disease  of  guavas.2  It  can  readily  be  grown  and 
fruited  in  the  laboratory  as  a  saprophyte  on  the  most  various  sub- 
stances, including  all  the  standard  media  used  for  bacterial  cultures. 
There  are  two  kinds  of  fruiting  or  two  methods  of  spore-pro- 
duction. The  one  upon  which  the  generic  term  Glceosporium  is 
founded  is  by  far  the  most  common,  and  is  that  upon  which  the 
identification  of  the  parasite  is  made  in  the  field.  This  it  is  which 
is  seen  on  green  or  ripe  apples,  and  more  commonly  this  only  is 
found  in  the  cankered  spots  of  the  apple-tree  limbs.  In  these  and 
other  situations  the  mycelium  which  vegetates  in  the  tissues  of  the 
host,  often  penetrating  deeply  therein,  forms  in  minute  specialized 
areas  little  cushions  of  interlaced  threads  just  beneath  the  surface, 
and  from  these  cushions  numerous,  closely  associated,  erect  threads 
(sporophores)  arise,  on  the  apices  of  which  spores  (conidia)  are 
produced  by  abstriction.  That  is,  the  terminal  portion  of  one  of 
the  filamentous  sporophores  is  separated  by  the  formation,  a  little 
below  the  apex,  of  a  cross  partition,  and  at  the  same  time  or  closely 
thereafter  the  side  walls  at  this  place  are  contracted  as  though  by 
a  strangulating  thread.  The  part  above  the  partition  and  constric- 
tion becomes  the  conidial  spore  and*when  mature  this  spontaneously 
separates  from  its  parent  filament  (PI.  II.  Fig.  2  and  PI.  VI.,  Fig. 
i).  The  same  process  may  take  place  many  times,  conidium  after 
conidium  being  formed  from  the  same  sporophore.  On  the  apple  and 
other  fruits  the  little  localized  masses  of  sporophores  forming  what 
are  called  sori,  push  up  the  epidermis  from  beneath  until  it  rup- 
tures, making  a  pustule,  which  may  be  discerned  by  the  unaided 
eye.  The  unopened  pustules  are  black,  due  to  the  dark  color  of  the 
fruiting  threads,  and  not  infrequently  the  dark-olive  colored  my- 
celium grows  in  dense  mats  or  masses,  outside  the  substance  in 
which  it  derives  its  nutriment;  but  the  spores  issue  from  the  rup- 
tures in  pinkish  masses  and  are  then  still  easier  seen  by  unaided 
vision.  Very  often  the  spore-pustules  are  arranged  in  several  con- 
centric lines  best  seen  towards  the  borders  of  the  infected  spots  on 
the  fruit.  These  spots  from  a  small  beginning  constantly  increase  in 
size  until  perhaps  half  or  more  of  the  apple  is  involved ;  or  several 
spots,  originally  distinct,  coalesce  into  one  large  area  of  infection. 
These  circular  spots,  blackish  in  color,  somewhat  depressed,  with 
their  concentric  rings  of  spore-pustules  and  the  pinkish  spore- 
masses,  clearly  characterize  the  malady  and  serve  definitely  to  dis- 

1.  Sheldon,  John  L.     Concerning  the  Identity  of  the  funjri  Causing-  an  Anthracnose  of  the 
Sweet  Pea  and  the  Bitter-Rot  of  the  Apple.    Science,  N.  S.  22:51.     Jan.  1905. 

2.  Sheldon,  John  L.    Ripe  Rot  or  Mummy  Disease  of  Guavas.     l!ul.  W,  Va.  Aer.  EXD   Sta 
94:297-315.     Ap.  1906. 


1907.}        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  559 

tinguish  the  disease  from  any  other  such  fruit  infection.  (PI.  III., 
Fig.  2.) 

The  spores  as  they  issue  from  a  pustule  are  imbedded  in  an  ad- 
hesive substance  so  that  they  remain  in  a  coherent  body,  sometimes 
taking  the  shape  of  a  curled  tendril-like  thread,  more  often  of  an 
irregularly  rounded  globule.  After  exposure  to  dry  air  the  cement- 
ing substance  becomes  hard,  but  is  quickly  dissolved  again  in  water. 
When  once  thus  separated  in  water  the  spores  lose  this  cohesive 
peculiarity.  Under  proper  conditions  of  temperature  and  moisture 
they  quickly  germinate  by  sending  out  one  or  more  thread-like 
tubes,  and  these,  in  artificial  cultures,  soon  begin  to  produce  a  new 
generation  of  spores  like  those  from  which  the  threads  originated. 
All  this  may  occur  within  24  to  48  hours  in  a  glass  tube  or  dish. 

In  such  cultures  there  are  frequently  seen  at  the  tips  of  germinal 
threads  peculiar,  dark  colored,  spore-like  bodies,  the  nature  and  of- 
fice of  which  have  been  considerably  discussed.  Recently  Hassel- 
bring  has  shown  that  they  are  specialized  organs,  called  appressoria 
by  Frank  of  Germany,  for  adhesion  to  smooth  surfaces  like  those  of 
fruits,  and  for  aid  in  the  penetration  of  the  epidermis  by  the  germi- 
nal tube  which  each  emits.1  The  appressoria  are  produced  on  the 
conidial  germ-tubes  when  these  touch  a  solid  body  not  bathed  in 
nutritient  liquid.  They  seem,  therefore,  to  play  an  important  role 
in  the  infection  of  apples  (PI.  X). 

While  the  conidia  are  protected  by  the  substance  which  causes 
them  to  cohere  as  they  issue  from  the  spore-pustules,  they  preserve 
their  vitality  a  long  time  when  they  are  kept  in  a  dry  place;  but 
they  very  soon  lose  the  power  of  germination  if  the  readily  soluble 
protecting  substance  is  first  washed  away.  In  laboratory  experi- 
ments fresh  spores  placed  in  tap  water  and  at  once  filtered  out  and 
dried  for  24  hours  fail  to  germinate  when  again  moistened.  As 
indicated  above,  the  germination  of  viable  conidia  is  very  prompt 
when  conditions  are  favorable  and  they  were  favorable  in  these  tests. 

Notwithstanding  the  ordinary  name  this  fungus  does  not  cause 
a  true  rot,  as  has  been  stated  above.  The  apple  substance  does  not 
become  soft,  but  becomes  instead  tough,  and  at  length  dry  and  hard. 
Other  fungi  may  simultaneously  or  subsequently  invade  the  tissues 
and  break  down  the  structure,  but  the  effect  of  this  parasite  is  a 
preservative  one  upon  the  cell  walls.  When  infected  apples  dry  and 
harden  into  the  shriveled  state  usually  called  mummies,  the  vege- 
tative threads  (mycelium)  of  the  fungus  and  the  cushion  of  erect, 


1.  Hasselbring,  Heinrich.    The  Appressoria  of  the  Anthracnoses.  Bot.  Gaz.  42:135-142.  Aug. 
1906.' 


560  BULLETIN  No.  118.  [September, 

crowded,  spore-bearing  filaments  (sporophores)  retain  their  vitality 
for  a  long  time — one  or  more  years  if  kept  dry — and  pinkish  masses 
of  spores  are  promptly  formed  again  within  about  three  to  six  days 
after  sufficient  moisture  is  supplied.  The  spores  (conidia)  are  pro- 
duced on  the  tips  of  the  old  sporophores  as  they  may  have  been 
months  before. 

In  this  way  certain  of  the  old  mummies  become  sources  of  in- 
fection the  season  after  they  are  formed,  (PL  VIII.,  Fig.  2)  but  it 
will  be  shown  later  that  this  is  true  only  when  the  old  fruits  are 
not  destroyed  by  other  rots;  that  is,  only  when  they  have  been 
mummified  by  the  Gloeosporium  fungus  and  then  have  not  been 
subject  to  the  attack  of  bacteria,  molds,  or  other  saprophytic 
growths. 

The  fungus  lives  over  winter  in  wound-like  spots  called  cankers 
on  the  limbs  of  the  apple  trees,  and  from  these  infection  may  start 
the  succeeding  season.  Not  infrequently  the  location  of  a  canker 
can  be  made  out  by  the  spots  beneath  it  on  the  growing  fruit,  caused 
by  spores  washing  with  rain  water  from  the  former  onto  the  sur- 
faces of  the  apples.  The  area  of  such  infection  in  a  well-fruited 
tree  frequently  takes  the  form  of  a  cone  with  its  apex  upward  at  or 
beneath  the  limb-canker.  The  water  carrying  the  spores  does  not 
descend  perpendicularly  because  of  the  interference  of  the  foliage, 
hence  the  wider  area  of  infection  below. 

The  fungus  in  the  cankers  grows  and  fruits  just  as  it  does 
in  the  apples,  (PL  II.)  although  the  spore-pustules  do  not  show 
much,  i.  e.  are  not  very  evident,  before  the  spores  exude  and  they 
are  not  arranged  in  concentric  circles,  owing  in  both  cases  to  the 
nature  of  the  substratum.  The  method  of  production  of  the  conidia 
and  the  conidia  themselves  are  the  same.  The  latter  exude  in  pink- 
ish, (sometimes  showing  shades  of  yellow  instead,)  adhesive  tendrils 
or  irregular  heaps,  indistinguishable  from  those  on  the  fruit.  There 
is  likewise  no  difference  in  the  behavior  of  the  conidia  in  germina- 
tion, etc.  It  is  to  be  noted,  however,  that  the  spore-masses  exude 
only  when  the  bark  has  been  moistened  by  water  or  when  the  air 
continues  very  moist  for  some  days. 

The  second  spore-form  or  Glomerella  stage  is  readily  secured 
in  laboratory  cultures,  but  is  not  very  commonly  found  in  nature. 
It  was  first  discovered  by  Clinton1,  in  1901,  in  cultures  and  then 
on  old,  infected  apples  which  were  kept  for  some  time  in  a  moist 
chamber.  Hasselbring2  (1901-02)  made  special  studies  for  this 

1    Clinton,  G.  P..  Apple  Rots  in  Illinois.    Bui.  111.  Apr.  Exp.  Sta.  69:206. 

2.  Burrill,  T.  J.,  and  Blair,  J.  C.  Bitter  Rot  of  Apples.    Bui.  111.  Agr.  Exp.  Sta.  77:354. 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  561 

purpose  of  old  mummies,  but  failed  to  find  again  this  form.  It  has 
not  been  found  by  the  author  in  numerous  examinations  on  fruits 
kept  out  of  doors.  Spaulding1  found  this  asco-fruit  in  rotting  ap- 
ples kept  in  the  laboratory  and  in  artificially  produced  limb-cankers, 
and  Scott2  reports  it  from  infected  apples  kept  in  the  laboratory  as 
well  as  in  artificial  cultures.  From  natural  cankers  cut  on  July 
28,  1905,  and  again  on  August  21,  same  year,  Barrett  (PL  I,  Fig.  2, 
and  PI.  VI.,  Fig.  2)  found  perithecia  and  asci  with  ascospores. 
This  suffices  to  show  that  the  second,  perfect,  or  asco-fruit  does 
develop  at  times  and  under  certain  conditions,  but  the  Glomerella 
stage 'surely  does  not  play  any  important  role  in  the  seasonal  de- 
velopment or  dissemination  of  the  fungus,  as  was  at  one  time  sup- 
posed. 

The  ascospores  are  altogether  similar  to  the  conidia  in  appear- 
ance, structure,  and  reproductive  characteristics.  They  germinate 
as  readily  whenever  conditions  favor  and  they  die  as  soon  under 
unfavorable  circumstances.  They  have  no  more  resistance  to  ex- 
ternal vicissitudes  and  are  therefore  not  specialized  to  carry  the 
fungus  over  winter.  It  is  the  mycelium  both  in  the  mummies  and 
the  cankers  which  retains  vitality  and  which  upon  the  recurrence  of 
favorable  conditions  produces,  again  and  again,  crops  of  conidia. 
It  was  Hasselbring3  who  first  proved  this  to  be  true  of  the  mummied 
fruits,  though  it  was  previously  very  generally  assumed  that  in  some 
way  these  old  infected  apples  carried  the  fungus  over  the  winter. 
That  the  same  thing  occurred  in  regard  to  the  limb-cankers  was 
evident  upon  the  first  examination  made  upon  them4  and  abundant 
verification  for  both  observations  have  since  been  made. 

It  has,  however,  been  found  that  the  early  statements  to  the  ef- 
fect that  the  cankers  are  limited  to  one  year's  growth  is  not  always 
true.  Sometimes  the  mycelium  remains  alive  a  second,  or  even  a  third 
year,  in  the  border  around  the  originally  infected  area,  or  it  may  be 
re-infection  takes  place  due  to  the  wound-like  character  of  the  first 
canker.  Plate  VIII.,  Fig.  i,  shows  a  canker  two  years  old  which, 
after  the  limb  was  cut,  produced  spores  from  the  portion  which  en- 
circles the  central  area  killed  by  the  fungus  the  first  year. 

In  the  case  of  the  mummies  it  will  be  seen  later  that  the  con- 
clusions commonly  reached  from  the  earlier  studies  need  some  mod- 
ification, but  our  information  still  points  to  them  and  to  the  cankers 

1.  Von  Schrenk,  H.,  and  Spaulding-,  P.,  The  Bitter  Rot  of  Apples.    Bui.  U.  S.  Dept.  ACT.: 
Bul.Plt.  Ind.  44:24. 

2.  Scott,  W.  M.,  The  Control  of  Apple  Bitter  Rot.Bul.    U.  S.  Dept.  Agr.;  Bui.  Pit.  Ind.  93:10 
Mar.  1906. 

3.  Hasselbring-,  H.,  The  Bitter  Rot  and  its  Control.    Trans.  111.  Hort.  Soc.  33:350.    1902,  and 
Bui.  111.  Atfr.  Exp.  Sta.  77:354,  1902. 

4.  Ibid,  page  355. 


562  BULLETIN  No.  118. 

as  the  sources  of  infection  as  the  new  season  arrives,  and  to  the 
living  mycelium  in  these  mummies  and  cankers  as  the  agent  of  per- 
petuation. When  the  weather  conditions  become  suitable,  from 
June  to  October,  the  previously  dormant  mycelium  becomes  active 
again  and  soon  furnishes  an  abundant  crop  of  conidial  spores,  in 
the  familiar  pinkish,  waxy  masses.  Possibly,  too,  asci  and  asco- 
spores  may  be  produced  in  such  successive  manner,  but  if  so  the 
occurrences  must  be  far  less  common  and  the  spores  far  less  numer- 
ous. They  are  not  often  encountered  in  nature  when  direct  search 
is  made.  It  has  been  shown  above,  however,  that  this  second  or 
Glomerella  stage  is  of  small  importance  as  a  practical  matter.  It 
adds  nothing  to  the  persistence  of  vitality  nor  to  the  possibilities  of 
starting  a  new  outbreak  of  the  disease.  The  two  kinds  of  spores  are 
altogether  similar  in  structure,  and  in  function  there  is  no  difference 
that  can  be  determined. 

PART  II    SPECIAL  INVESTIGATIONS 

The  account  given  upon  preceding  pages  represents  fairly  well 
public  information  upon  the  growth  and  development  or  life  his- 
tory of  the  fungus  under  consideration.  More  details  can  be  found 
in  the  citations,  but  whether  references  have  or  have  not  been  made 
everything  stated  is  upon  the  authority  of  or  agrees  with  the  writ- 
er's personal  observations  and  studies,  except  that  the  office  and 
mode  of  action  of  the  appressoria  are  quoted  from  the  writer  cited. 

This  does  not  mean,  however,  that  everything  needful  concerning 
the  life  history  of  the  parasite  had  heretofore  been  ascertained  and 
made  known,  or  that  additions  of  great  importance  may  not  be 
made.  There  are  now  to  be  given  the  further  results  of  studies  up- 
on special  points  in  the  developmental  history  of  the  fungus,  knowl- 
edge of  which  has  been  deemed  necessary  before  fully  intelligent 
warfare  can  be  prosecuted.  In  the  statement  some  facts  heretofore 
well  known  must  be  recounted,  but  it  will  not  be  difficult  for  the 
reader  to  distinguish  these  from  those  now  reported  for  the  first 
time. 

ORIGIN  OF  LIMB  CANKERS 

Limb  infections  (cankers)  originate  in  wounds  (PL  I.,  Fig.  i, 
PI.  VII.,  Fig.  2).  While  cankers  are  very  easily  produced  artifi- 
cially by  mechanical  punctures  and  the  insertion  of  conidia  taken 
from  the  pustules  of  infected  fruit  and  from  pure  cultures,  no  posi- 
tive results  have  been  obtained  by  placing  such  conidia  on  the  stir- 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  563 

face  of  uninjured  bark,  whatever  the  age  of  the  twig  or  limb.  It 
is  often  observed  that  a  cankered  area  has  at  or  near  its  center  a 
little  dead  twig,  or  the  evidence  of  one  having  been  there.  This  is 
especialy  true  in  regard  to  those  varieties  of  apples  which  are  more 
than  others  subject  to  twig  blight,  like  the  Jonathan  and  Willow. 
Sometimes  there  may  be  found  at  the  base  of  the  portion  of  a  twig 
killed  by  blight  a  small  area  infected  by  the  rot  fungus,  the  latter 
evidently  having  started  in  the  dead  or  dying  bark  and  descended  in 
the  tissues  to  the  living  parts.  Here,  as  elsewhere,  the  fungus  shows 
its  saprophytic  proclivities.  But  it  is  wide  of  the  mark  to  infer  from 
such  observations  that  it  does  not  also  possess  vigorous  parasitic 
powers ;  on  rapidly  growing  fruits  it  needs  no  aid  except  favorable 
external  conditions  either  in  the  penetration  of  the  epidermis  or 
the  subjugation  of  the  living  tissues.  It  simply  is  not  able  to  make 
entrance  through  the  exterior  protecting  coating  of  the  uninjured 
bark  of  a  living  branch  without  mechanical  help,  but  such  bruises  as 
made  by  hail  are  sometimes  sufficient  aid.  It  may  be  added  here  that 
fruit  spurs  which  have  scars  left  by  the  separation  of  fruit  stem  the 
preceding  year,  are  open  to  infection  and  may  bear  small  cankers 
of  the  bitter  rot  fungus  (PL  IV.,  Fig.  2). 

Cankers  may  be  started  as  late  in  the  season  as  the  weather  con- 
ditions permit  the  growth-  of  the  fungus.  These  conditions  often 
exist  at  or  after  the  time  of  picking  the  apples,  and  limb  bruises  then 
made  may  become  cankers  to  serve  as  sources  of  infection  the  fol- 
lowing year.  When  orchard  managers,  becoming  impatient  with 
the  slow  process  of  hand  picking,  resort  to  thrashing  off  rotting 
apples  with  the  idea  of  preventing  further  infection,  they  are  un- 
consciously arranging  for  a  fine  crop  of  cankers  the  next  season; 
the  bruises  thus  made  on  the  bark  of  limbs  open  the  way  for  the 
development  of  the  fungus. 

It  must  be  admitted,  however,  that  we  cannot  yet  explain  why 
so  many  more  cankers  are  formed  at  one  time  than  another,  in  one 
season  than  another,  beyond  accounting  for  by  the  prevalence  of  the 
disease  on  the  fruit,  the  comparison  of  climatic  conditions,  the 
handling  of  the  trees,  etc.  During  the  season  when  the  existence  of 
limb-cankers  was  first  made  known1,  they  were  found  in  large  num- 
bers in  many  orchards  of  Southern  Illinois.  Never  since  that  year 
(1902)  have  they  been  so  generally  abundant.  While  it  has  been 
easy,  one  year  as  well  as  another,  to  produce  them  artificially, 

1.  Burrill,  T.  J  ,  and  Blair,  J.  C.  Prevention  of  Bitter  Rot.  Cir.  111.  Agr.  Exp.  Sla.,  58: 
Jul.1902.  Same,  Bitter  Rot  of  Apples.  Bui.  111.  Afrr.  Exp.  Sta.,  77:354,  Jul.  1902.  Von  Schrenk, 
H.,  and  Spaulding-,  P.,  The  Bitter  Rot  of  Apples,  Bui.  U.  S.  Dept.  Agr.,  Bui.  Pit.  Ind.  44:29,  Jul. 
iyu3. 


564  BULLETIN  No.  118.  [/September, 

(PI.  II.,  Fig.  i,  PI.  IV.,  Fig.  i,)  during  some  seasons  it  has  been 
hard  to  find  natural  ones  containing  the  living  fungus  except  upon 
some  few  trees.  In  some  sections  of  the  country1  this  seems  to  be 
always  the  case. 

FIELD  AND  LABORATORY  DATA 

July  II,  1903,  inoculated  a  limb  of  a  Willow  apple  tree  with  bitter  rot  spores. 
August  II  the  canker  was  four  inches  long  and  many  black  sori  were  being 
formed  under  the  surface.  Three  weeks  later  the  canker  had  grown  to  be  ten 
and  one-half  inches  long  and  had  encircled  more  than  half  of  the  limb  which 
was  seven-eighths  of  an  inch  in  diameter.  This  is  the  canker  later  used  in  ex- 
periments 2  and  4  under  treatment  of  cankers. 

Inoculated  on  July  27  three  more  limbs  of  a  Willow  apple  tree  with  bitter 
rot  spores.  All  three  inoculations  produced  cankers. 

Inoculated  three  limbs  of  a  Willow  apple  on  July  30.  The  bark  of  one  limb 
was  slit,  that  of  the  other  two  was  bruised.  After  inoculation  the  wounds  were 
wrapped  with  damp  cloths.  All  developed  cankers  and  produced  cushions  of 
hyphae. 

August  7,  inoculated  two  limbs  of  a  Willow  apple  tree  with  bitter  rot  spores. 
Both  produced  cankers. 

July  II,  1904,  inoculated  limb  of  young  apple,  (2  years  out)  and  July  28  a 
canker  iH  inches  long  had  formed.  It  was  dark,  very  much  sunken,  and  sori 
were  evidently  forming  under  the  surface.  On  same  date  another  limb  was 
inoculated  and  July  28,  a  canker  one  inch  long  had  developed  and  bore  same 
small  elevations.  The  canker  became  three  inches  long  and  was  cut  March  n, 
1905.  Other  inoculations  made  on  same  date  were  followed  with  cankers  which 
on  July  28  were  in  length  respectively  as  follows :  I  inch ;  I  inch,  with  sori ;  I 
inch,  with  sori;  i  inch,  with  sori;  1/4  inch,  with  sori;.  2^4  inches,  with  sori. 

July  15,  1904.  The  bark  of  4  limbs  of  Willow  apple  tree  was  bruised  and 
spores  inserted,  with  results  as  follows:  (i)  A  small  canker  developed;  (2) 
slight  development,  but  no  canker;  (3)  no  canker;  (4)  a  small  canker  formed. 

July  28,  1904.  Inoculation  on  a  pear  limb  produced  a  slight  development, 
but  no  canker. 

August  12,  three  limbs  of  Willow  apple  tree  were  inoculated  with  bitter  rot 
spores.  All  three  inoculations  produced  cankers. 

August  18,  three  limbs  of  unknown  variety  were  inoculated  with  bitter  rot 
spores.  All  produced  small  cankers. 

September  i,  two  limbs  of  a  Willow  apple  tree  were  inoculated  with  bitter 
rot  spores.  Small  cankers  were  produced. 

September  12,  two  limbs  of  a  Willow  apple  tree  were  inoculated.  Both 
developed  small  cankers. 

September  12,  inoculated  a  limb  of  apple  of  unknown  variety.  October  3, 
there  was  a  small  canker. 

September  15,  inoculated  several  twigs  of  Willow  apple.  October  3,  all  show 
considerable  development. 

September  22,  inoculated  two  Willow  apple  limbs.  October  3,  some  devel- 
opment. 

September  24,  inoculated  three  branches  of  a  Willow  apple  tree.  No  devel- 
opment took  place. 

September  30,  inoculated  three  limbs  of  an  unknown  variety  with  bitter  rot 
spores.  No  development  took  place. 


1.  Alwood,  Wm.  B.,  Orchard  Studies.    Bui.  Va.  Agr.  Exp.  Sta.  142:265  N.  1902. 


1907. J         BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  565 

EFFECTS  OF  CHEMICALS  ON  SPORES  AND  ON  CANKERS 

It  was  deemed  worth  while  to  make  some  careful  tests  upon  the 
strength  of  fungicides  which  are  necessary  to  kill  the  spores  for 
such  aid  as  might  thereby  be  furnished  for  practical  work  in  the 
field.  Since  Bordeaux  mixture  holds  in  suspension  solid  particles 
which  interfere  with  microscopic  examinations,  solutions  in  water 
of  copper  sulfate  were  used  instead.  It  is, known  that  the  copper 
is  the  chief  agent"  that  gives  Bordeaux  mixture  its  effectiveness  as 
a  spray,  hence  the  copper  solutions  may  be  taken  to  apply  well  to 
the  action  of  the  more  commonly  used  mixture.  The  results  to  be 
reported  certainly  give  abundant  reason  for  the  effectiveness  of 
the  Bordeaux  spray. 

The  laboratory  tests  show  that  solutions  of  copper  sulfate  in 
distilled,  or  ordinary  rain-water,  in  amounts  above  I  to  1,000,000 
parts  prevent  the  germination  of  spores  recently  matured  in  all  cases 
when  there  is  considerable  of  the  solution  applied.  When,  however, 
the  quantity  of  the  latter  is  much  reduced  the  effect  is  not  so  cer- 
tain. Further  tests  show  that  the  presence  of  organic  compounds 
in  the  solutions  greatly  reduce  the  fungicidal  action.  For  instance, 
when  copper  sulfate  is  added  to  weak  beef-broth  (bouillon  one- 
half  standard  strength)  instead  of  to  water,  germination  of  spores 
immersed  therein  is  not  prevented  in  a  strength  of  the  solution  up 
to  i  part  of  the  copper  compound  to  1000  of  the  broth.  That  is,  it 
requires  more  than  1000  times  as  much  of  the  copper  in  weak  broth 
as  it  does  in  water  to  kill  the  spores  of  this  fungus.  The  explana- 
tion probably  is  that  some  combination  takes  place  between  the  cop- 
per salt  and  the  organic  compounds,  rendering  the  former  inert.  It 
seems  that  something  similar  takes  place  when  quantities  of  these 
spores  are  substituted  for  the  organic  matter  of  the  broth,  for  when 
approximately  the  same  small  quantity  of  spore-mass  is  placed  in 
one  medium-sized  drop  of  copper  sulfate  solution  the  proportion 
of  the  copper  salt,  to  be  effective,  must  be  not  less  than  I  to  loo.ono 
parts  of  water,  while  in  one  hundred  drops  (4  cc.)  similar  killing 
effect  occurs  in  a  solution  containing  i  part  of  copper  sulphate  to 
400,000  parts  of  water  (see  data  following,  Expts.  7  and  8). 
(PI.  X).  It  is  plain,  therefore,  that  the  liquid  used  as  a  spray  must 
be  very  considerably  stronger  than  the  laboratory  tests,  ao  com- 
monly conducted,  indicate,  and  a  larger  quantity  of  a  given  solution 
will  be  more  certain  than  will  a  smaller  amount  to  kill  the  spores 
with  which  the  liquid  comes  in  contact.  The  copper  compound  as 
dry  dust  has  no  effect  whatever,  but  the  spores  in  that  case  could 
not  germinate  for  the  want  of  moisture. 


566  BULLETIN  No.  118.  [September, 

Since  common  salt  (sodium  chlorid)  has  been  advocated  as 
useful  in  controlling  bitter  rot,  it  was  deemed  best  to  determine 
what  its  action  is  upon  the  spores.  Experiment  soon  showed  that 
a  watery  solution  of  this  substance  does  have  very  considerable  ef- 
fect (see  Expts.  12  and  13  following).  When  fresh  spores  are  im- 
mersed in  3  parts  of  the  salt  to  1000  of  water  germination  does  not 
take  place,  but  if  the  proportion  is  reduced  to  2.5  to  1000  the  germ 
tubes  are  emitted  and  growth,  evidently  not  quite  normal,  is  con- 
tinued. This  then  seems  to  be  the  crucial  point  when  there  is  a  con- 
siderable amount  of  the  solution.  It  is  probable  that  the  facts  found 
to  be  true  in  this  case  of  copper  sulfate  will  hold  here  too  for  small 
quantities  of  the  solution  and  for  a  spray  or  even  a  wash  stronger 
solutions  would  be  required  to  prevent  spore  development,  and  then 
serious  damage  to  the  foliage  may  follow. 

It  would  be  very  helpful  if  some  way  could  be  found  to  render 
the  limb-cankers  innoxious  without  injuring  the  tree  on  which  they 
are  found.  The  first  thing  to  be  thought  of  is  a  spray  or  wash  of 
some  substance  destructive  to  the  fungus,  and  copper  sulfate  and 
Bordeaux  mixture  naturally  first  present  themselves  to  the  mind 
of  the  experimenter. 

It  is  evidently  necessary  to  have  some  exact  knowledge  of  the 
existence  of  the.  living  fungus  in  the  tissues  of  a  canker  before  any 
inference  can  be  drawn  as  to  the  positive  effect  of  an  application  to 
the  exterior  surface.  The  plan  adopted  for  the  tests  herein  reported 
was  to  submit  the  cankers  to  conditions  favorable  to  the  formation 
and  exudation  of  these  spores  without  at  the  same  time  encouraging 
too  much  growth  of  molds,  etc.  After  trying  several  methods  the 
procedure  adopted  was  to  soak  the  cankered  limbs  freshly  cut  from 
the  trees  for  a  few  hours,  or  those  that  had  been  severed  some 
weeks  or  months  before,  for  a  longer  time  usually  24  hours,  in 
ordinary  tap  water  and  then  to  keep  them,  often  wrapped  in  moist 
paper,  in  a  closely  covered  tin  box  placed  in  a  warm  room  (prefer- 
ably ctMiit  26°  to  30°  C.)  It  was  found  that  the  pinkish  spore- 
masses  usually  appeared  in  from  three  to  six  days,  giving  clear  evi- 
dence of  the  activity  of  the  fungus  and  definitely  announcing  its 
identity.  (PI.  II.,  Fig.  i). 

Then  to  test  the  efficiency  of  external  applications,  selected  cank- 
ers were  cut  transversely  through  the  middle  and  one-half  was  kept 
for  a^check  without- treatment,  while  on  the  other  half  the  fungi- 
cidal  wash  under  test  was  applied,  after  which  both  parts  were 
treated  alike  for  the  development  of  spores.  In  some  cases  the  di- 
vision of  the  cankers  was  made  before  the  soaking,  in  some  cases 


1907.}        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  567 

subsequently.  The  substances  used  were  copper  sulphate  in  the  pro- 
portion of  6  pounds  to  50  gallons  of  water;  thick  Bordeaux  mix- 
ture; copper  carbonate  12^  ounces  (with  ammonia  water  7^ 
parts)  to  50  gallons  of  water;  and  Oregon  wash  after  the  formula : 
sulfur  15  pounds,  copper  sulfate  20  ounces,  slacked  lime  15  pounds 
to  50  gallons  of  water. 

None  of  the  experiments  tried  (see  Expts.  1-17  following  un- 
der "Treatment  of  Cankers,"  etc.)  gave  encouragment  for 
the  hope  that  any  such  application  to  the  tree  can  be  of  any  prac- 
tical importance  in  destroying  the  cankers  or  in  controlling  the 
disease.  This  is  disappointing,  for  it  must  be  acknowledged  that 
it  is  impossible  to  find  and  remove  by  the  knife  or  other  pruning 
implement  all  of  the  infected  spots  on  the  limbs,  shoots,  and  fruit- 
spurs.  After  the  position  of  the  canker  is  announced  by  the  spots 
on  the  fruit,  when  this  evidence  does  sufficiently  show,  it  is  too  late 
for  best  results  and  the  cone-shaped  figure  in  the  tree  is  not  always 
traceable.  The  preventive  method  of  cutting  out  the  cankers  is  not, 
therefore,  altogether  effective;  but  nothing  better  has  been  devised 
towards  suppressing  the  pernicious  part  they  play  in  starting  infec- 
tion upon  the  fruit. 

The  same  may  be  said  concerning  any  mummied  fruit  which 
serve  as  a  wintering  place  for  the  fungus.  Their  collection  by  hand 
seems  to  be  the  only  way  to  secure  the  destruction  of  the  infecting 
agent. 

FIELD  AND  LABORATORY  DATA 

Copper  sulfate.  For  the  most  part  the  following  described  cultures  were 
made  in  Syracuse  watch  glasses  and  kept  at  room  temperature,  about  24  C : 

Experiment  I.  This  experiment  consisted  of  four  cultures  of  the  following 
proportions  of  copper  sulfate  to  water:  1:125,  6:1000,  1:200,  and  1:250.  Each 
culture  was  inoculated  with  as  nearly  as  could  be  estimated  the  same  quantity 
of  bitter  rot  spores.  At  the  end  of  48  hours  no  germination  had  taken  place  in 
any  of  the  cultures.  A  duplication  of  these  cultures  with  newly  formed  spores 
gave  a  similar  result. 

Experiment  2.  In  experiment  i  distilled  water  was  used  in  making  up  the 
solutions.  In  this  experiment  the  same  percentage  solutions  were  made  up  with 
rain-water  and  inoculated  with  spores.  After  24  hours  aside  from  the  swelling 
of  a  few  spores  in  the  weakest  solution,  there  was  no  indication  of  a  tendency 
to  germinate.  Germination  was  good  in  a  rain-water  check  culture. 

Experiment  3.  The  following  copper  sulfate  solutions  were  made  up  and 
inoculated  with  bitter  rot  spores:  i :  10,000,  1:100,000,  1:1,000,000,  and  1:10,000,- 
ooo.  A  check  culture  was  made  with  distilled  water  and  one  with  half  rain- 
water and  half  bouillon.  In  three  days  no  spores  had  germinated  in  the  two  strong- 
est solutions  but  a  few  spores  in  the  i :  i,ooo,oco  solution  had  sent  out  very  short, 
weak  germ  tubes  which  were  apparently  dead  and  the  protoplasm  somewhat  dis- 
integrated. The  few  germinated  spores  in  the  1:10,000,000  solution  were  still 
alive,  but  very  little  growth  was  taking  place.  They  eventually  died.  The  spores 
which  had  germinated  in  the  two  last  named  cultures  were  mostly  spores  float- 
ing on  the  surface  of  the  liquid.  A  few  appressoria  were  produced  by  the  sub- 


568  BULLETIN  No.  118.  [September, 

merged,  germinated  spores,  but  none  by  those  on  the  surface.  Germination  in 
distilled  water  was  fair  and  here  it  was  particularly  noticeable  that  the  spores 
in  contact  with  the  bottom  of  the  dish  produced  appressoria.  Germination  in  the 
bouillon  and  rain-water  was  very  good. 

Experiment  4.  This  experiment  was  made  for  the  purpose  of  determining 
what  effect  a  nutrient  solution  in  the  presence  of  copper  sulfate  solutions  would 
have  on  the  germination  of  the  spores.  Standard  bouillon  diluted  with  an  equal 
amount  of  water  was  selected  as  the  nutrient  solution,  and  the  following  copper 
sulfate  solutions  were  made  up:  i  :iooo,  1:10,000,  1:100,000,  1:1,000,000,  and 
1:10,000,000.  The  check  was  standard  bouillon.  After  inoculation  the  cultures 
were  kept  at  26°  C.  In  24  hours  germination  was  pretty  good  in  each  culture, 
slightly  better  in  the  weaker  solutions  and  in  the  check.  Appressoria  were  com- 
mon except  with  the  floating  spores.  Bacteria  were  present  in  all  cultures,  a  fact 
which  seemed  to  indicate  that  the  copper  had  entered  into  combination  with  some 
of  the  substances  of  the  bouillon,  probably  the  proteids,  and  formed  an  insoluble 
compound.  Tests  for  soluble  copper  made  with  thin  slices  of  potato  and  potas- 
sium iodide  showed  it  to  be  present  in  slight  quantities  in  the  1 : 1,000,  and  I  :io,- 
ooo  solutions  only.  On  the  following  day  there  was  a  more  apparent  difference 
in  the  various  cultures,  particularly  in  the  growth  of  the  germ  tubes.  After 
germination  practically  no  growth  took  place  in  the  I  :i,ooo  culture,  while  in  the 
i :  10,000  solution  a  number  of  germ  tubes  which  had  originated  from  a  few 
masses  of  spores  were  growing  well  and  a  few  were  producing  new  spores. 

Experiment  7.  This  experiment  and  the  following  one  were  made  to  deter- 
mine, if  possible,  whether  or  not  the  amount  of  the  solution  influenced  the  toxic 
effect  on  the  germinating  spores.  In  other  words,  have  the  spores  or  newly 
formed  germ  tubes  an  accumulative  action  on  the  copper  in  solution?  In  this 
experiment  4  c.c.  of  each  of  the  following  copper  sulfate  solution  was  placed  in 
a  watch  glass  and  as  nearly  as  could  be  judged  the  same  amount  of  spores  added 
to  each:  1:100,000,  1:200,000,  1:400,000,  1:1,000,000,  1:2,000,000,  1:4,000,000, 
and  i :  10,000,000. 

In  24  hours  the  condition  was  as  follows : 

1:100,000,  no  germination,  some  spores  dying. 

1 :20O,ooo,  germination  slight,  no  continued  growth,  and  the  short  germ  tubes 
soon  became  hyaline  at  the  tip,  or  formed  an  irregular  shaped  appressoria. 

i  :400,ooo,  germination  slight.  A  few  germ  tubes  produce'd  a  length  equal 
to  or  a  little  longer  than  the  length  of  the  spore  and  then  produced  appressoria 
or  soon  died. 

i :  1,000,000  germination  fair.  Some  of  the  germ  tubes  attained  a  length  two 
to  three  times  that  of  the  spore,  some  produced  branched  tubes  while  others 
germinated  at  both  ends.  Most  of  the  tubes  developed  appressoria. 

i  :2,ooo,ooo,  germination  very  fair.  Some  germ  tubes  were  five  to  seven 
times  the  length  of  the  spore,  and  although  somewhat  slender,  were  apparently 
healthy.  Appressoria  were  common. 

i  :4,ooo,ooo,  germination  very  fair.  The  germ  tubes  in  this  culture  were 
about  as  those  in  the  preceding  culture ;  if  any  different  the  former  were  slightly 
shorter  as  a  whole. 

i :  10,000,000,  percent  of  germination  not  quite  so  high  as  the  last  named  cul- 
ture, but  the  growth  of  the  germ  tubes  better. 

Distilled  water.  Germination  and  growth  slightly  better  than  the  1 : 10,000,- 
ooo  culture. 

In  all  of  the  above  cultures  there  was  little  germination  or  increase  in 
growth  after  the  second  day.  After  appressoria  were  formed  growth  ceased,  as 
not  one  of  the  latter  was  seen  to  germinate. 

Experiment  8.  In  this  experiment  only  1-25  of  1  c.c.  of  each  solution  was 
used.  The  solutions  were  of  the  same  strength  as  those  used  in  experiment 
7,  and  approximately  the  same  amount  of  spores  was  used.  After  24  hours  the 
following  condition  existed: 

1:100,000.  A  few  spores  had  pushed  out  short  germ  tubes  which  were 
slender  and  somewhat  abnormal.  No  appressoria. 

i  :20O,ooo.  Germination  very  fair.  The  germ  tubes  were  three  to  four  times 
the  length  of  the  spores,  apparently  healthy,  and  some  of  them  branched.  Many 
appressoria  were  produced,  and  some  had  germinated  and  formed  a  second  ap- 
pressorium.  An  occasional  new  spore  had  been  cut  off. 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  569 

1 :400,ooo.  Germination  good.  Germ  tubes  fifteen  to  twenty  times  the  length 
of  the  spores  and  many  of  them  had  produced  one  and  some  two  appressoria. 
Newly  formed  spores  were  not  uncommon. 

i : i, oco.ooo.  Germination  very  good.  In  this  culture  the  germ  tubes  had 
become  somewhat  branched  and  some  of  the  short  lateral  branches  were  cutting 
off  spores.  Appressoria  were  present  but  not  so  abundant  as  in  the  above  men- 
tioned cultures. 

i  :2,ooo,ooo.  Germination  pretty  good.  Both  germination  and  growth  not 
so  good  as  the  two  preceding  cultures.  Appressoria  were  rather  abundant.  In 
a  few  cases  as  many  as  four  were  produced  on  the  same  tube. 

1 :4,ooo,ooo.  Percentage  of  germination  pretty  good.  Germ  tubes  consid- 
erably branched  "but  short,  not  much  longer  than  the  spore.  Many  appressoria 
present,  and  an  occasional  one  germinated. 

1:10,000,000.  Percentage  of  germination  a  little  less  than  the  1:4,000,000 
solution,  but  growth  somewhat  better.  Germ  tubes  were  sparsely  branched  and 
terminated  in  poorly  developed  appressoria. 

Distilled  water.  Germination  pretty  good,  but  growth  poor.  Germ  tubes 
three  to  five  times  the  length  of  the  spores,  slender,  and  many  of  them  bearing 
one  to  two  appressoria. 

The  results  of  the  two  experiments,  7  and  8,  show  that  the  germination  and 
subsequent  growth  is  considerably  poorer  in  the  cultures  containing  the  larger 
amounts  of  the  copper  sulfate  solutions.  When  4  c.c.  of  the  liquid  is  used  a 
i  :400,ooo  strength  is  sufficient  to  prevent  the  germination  of  most  of  a  large 
number  of  spores  and  to  kill  those  which  do  have  any  tendency  to  grow.  If  a 
smaller  amount  of  the  solution  is  taken,  for  instance,  one  small  drop  (1-25  c.c.), 
the  toxic  effect  is  much  less  on  approximately  the  same  number  of  spores  as  was 
used  with  the  larger  amount.  A  weaker  solution  than  1:100,000  is  unsafe  when 
very  small  quantities  have  access  to  very  many  spores.  In  4  c.c.  of  a  1 :400,ooo 
solution  of  copper  sulfate  there  is  .0000025  gram  of  pure  copper.  In  1-25  c.c.  of  a 
.001  percent  solution  of  copper  sulfate  there  is  .0000001  gram  pure  copper. 

Experiment  9.  On  August  31  some  Bordeaux  mixture  was  washed  from  a 
number  of  leaves  on  a  tree  which  had  been  sprayed  on  August  12.  On  August 
27  there  was  a  heavy  shower,  but  aside  from  dews  there  was  no  other  moisture 
on  the  leaves.  Some  bitter  rot  spores  were  added  to  the  mixture  in  a  watch 
glass,  and  as  a  check  spores  were  aded  to  clear  rain-water.  In  three  days  no 
germination  had  taken  place  in  the  Bordeaux  mixture  washed  from  the  leaves, 
but  the  check  showed  both  good  germination  and  growth. 

Experiment  10.  Some  fresh  I  percent  Bordeaux  mixture  was  prepared  and 
inoculated  with  bitter  rot  spores.  No  germination  took  place. 

Experiment  n.  Some  Bordeaux  mixture  was  placed  on  two  cover  glasses 
and  allowed  to  dry  24  hours  when  they  were  remoistened  and  again  allowed  to 
dry  a  few  hours.  After  remoistening  a  second  time,  bitter  rot  spores  were 
added  and  the  cover  glasses  inverted  over  Van  Tieghem  cells.  In  three  days  no 
germination  had  taken  place. 

Experiment  12.  Six  cultures  were  instituted  with  the  following  sodium 
chlorid  solution:  1:200,  1:400,  1:1000,  1:2,000,  1 : 10,000,  1:20,000.  These  were 
inoculated  at  10  a.m.  with  spores  of  bitter  rot.  sc.c.  of  each  solution  was  used 
in  each  culture.  At  4  p.m.  there  was  no  germination  in  the  i :  200  and  i :  400 
solutions  but  was  good  in  the  next  two  weaker  solutions  and  fair  in  i :  10,000  and 
1:20,000  strengths.  Many  appressoria  were  produced.  At  9:30  a.m.  on  the  fol- 
lowing day  no  germination  had  taken  place  in  the  i  :20O  solution  and  only  a  few 
spores  had  started  to  germinate  in  the  next  weaker  strength.  Germination  was 
good  in  the  I  :i,ooo  and  1 :2,ooo,  fair  spores  of  the  1 :20,ooo  solution.  The  floating 
spores  of  this  culture  had  produced  long  germ  tubes. 

Experiment  13.  In  order  to  determine  more  nearly  the  minimum  strength 
of  sodium  chlorid  which  would  injure  the  spores  the  following  cultures  were 
made  and  5  c.c.  of  each  inoculated  with  bitter  rot  spores:  3:1,000,  1:400,  1:500, 
3:2,000,  i  :i,ooo.  After  24  hours  a  few  floating  spores  had  germinated,  but  none 
of  the  immersed  ones  in  the  3:1,000  strength.  In  the  second  strength  the  per- 
centage of  germination  was  small,  but  growth  was  pretty  good;  no  appressoria 
had  formed.  Germination  was  fair  in  the  i  :500  solution  as  was  also  the  growth. 
A  few  appressoria  had  formed.  In  the  3  :2,ooo  solution  germination  was  good, 


570  BULLETIN    No.  118.  [September, 

growth  rather  poor,  and  the  germ  tubes  short  and  bearing  appressoria.  The 
percentage  of  germination  in  1:1,000  solution  was  good,  growth  poor,  and  the 
germ  tubes  very  short  and  bearing  appressoria.  At  the  end  of  48  hours  the 
following  condition  existed : 

3:1,000.     No  germination  of  the  submerged  spores. 

1 1400.  A  s'mall  percent  of  the  submerged  spores  had  germinated  but  the 
germ  threads  were  long  and  somewhat  branched  and  in  some  cases  bearing 
appressoria  on  the  branches.  The  floating  spores  had  -formed  a  thin  film  of 
mycelium. 

1 1500.  Germination  fair,  growth  not  quite  as  good  as  the  1 1400  solution,  but 
appressoria  more  numerous. 

3 :2,ooo.  Germination  pretty  good,  growth  rather  poor,  germ  tubes  short 
and  almost  all  bore  appressoria.  The  floating  spores  had  rather  long  tubes. 

1 : 1,000.    Germination  good  but  growth  very  poor. 

TREATMENT  OF  CANKERS  AND  MUMMIES  TO  SHOW  VITALITY  OF  THE  FUNGUS, 

AND  TO  DESTROY  IT 

To  determine  the  persistence  of  vitality  of  the  fungus  in  cankers  they  were 
first  soaked  in  water,  when  deemed  necessary,  about  twenty-four  hours,  then 
wrapped  in  moist  paper  and  put  away  in  a  warm,  moist  place,  visually  in  a  rather 
tightly  closed  tin  box.  These  culture  experiments  were  made  with  many  cankers 
from  various  sources.  Some  of  them  were  artificially  inoculated,  but  by  far  the 
most  were  nnturally  formed.  Only  a  few  details  of  experiments  need  be  given. 

Experiment  I.  July  28,  1905,  a  canker  was  taken  from  a  tree  just  above 
two  infected  apples.  The  canker  was  treated  as  stated  above  and  on  the  fourth 
day  a  few  very  small  masses  of  pink  spores  were  seen.  An  examination  re- 
vealed the  fact  that  the  spores,  or  at  least  some  of  them,  were  coming  from 
perithecia,  in  which  asci  were  found.  Inoculations  with  these  ascospores  pro- 
duced typical  bitter  rot.  At  the  same  time  three  other  cankers,  one  taken  above 
two  infected  apples,  were  treated,  but  there  was  no  apparent  development  of 
the  fungus. 

Experiment  2.  In  this  case  three  cankers  were  used  that  had  been  taken 
from  a  Ben  Davis  tree  directly  above  an  infected  area.  They  were  soaked  and 
treated,  as  already  stated,  and  at  the  end  of  ten  days  all  three  were  producing 
pink  spores  of  bitter  rot.  On  one,  however,  several  perithecia  were  found  con- 
taining .mature  asci  and  ascospores. 

Experiment  3.  July  28,  a  canker  was  cut  from  a  Ben  Davis  tree  above  an 
infected  apple  and  treated  as  above.  On  August  5,  after  eight  days,  quite  a 
number  of  small  masses  of  spores  appeared. 

Experiment  4.  On  August  21,  twenty-one  cankers  representing  fifteen  in- 
fected areas  were  removed  from  about  fifteen  trees.  Seven  of  the  most  typical 
of  these  were  treated  as  explained.  After  five  days  two  were  producing  bitter 
rot  spores.  A  number  of  dead,  and  broken  twigs,  some  bearing  wounds,  small 
cankers,  etc.,  were  treated  at  the  same  time,  but  no  development  was  apparent. 

Experiment  5.  A  large  canker,  apparently  three  years  old  was  taken  from 
a  Willow  apple  tree  above  an  infected  area,  and  treated  as  all  others.  In  a  few 
days  a  number  of  pustules  of  pink  spores  appeared  and  inoculations  proved  them 
to  be  those  of  bitter  rot. 

Experiment  6.  On  July  28,  one  spur  and  one  canker  were  taken  from  a 
Ben  Davis  tree  above  an  infected  area.  After  ten  days  of  culturing1  the  spur 
produced  a  number  of  spore  masses  which  proved  to  be  of  bitter  rot. 

Experiment  7.  A  number  of  cankers,  produced  by  inoculation  during-  July, 
August,  and  September,  were  cut  from  trees  late  in  November,  and  the  most  of 
them  were  made  to  produce  spores  after  a  few  days  culture. 

Experiment  8.  March  II,  1905,  two  small  cankers  were  cut  from  a  small 
tree  in  the  University  orchard  and  brought  to  the  laboratory.  The  inoculations 
had  been  made  August  30,  1904,  on  small  branches  and  only  a  slight  development 
had  taken  place,  about  l/2  inch  in  length.  After  a  few  days'  culturing,  however, 
spores  were  produced  on  both  cankers  Nos.  214  and  222. 

Experiment  9.  On  August  21,  1905,  a  canker  one  and  one-half  inches  long 
and  on  a  limb  one  inch  in  diameter  was  cut  and  cultured.  The  canker  was  grow- 


1907.}        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  571 

ing  when  brought  into  the  laboratory.  At  the  end  of  three  days  both  sori  and 
perithecia  were  found. 

Experiment  10.  A  number  of  inoculations  were  made  on  limbs  of  Willow 
apple  tree,  without  breaking  the  epidermis.  The  spores  were  placed  on  the 
moistened,  smooth  bark,  and  the  limb  wrapped  with  a  moist  cloth.  The  latter 
was  moistened  from  time  to  time,  but  no  development  took  place. 

Experiment  n.  A  large  number  of  mummied  apples  were  collected  from 
trees  in  various  orchards  for  examination.  In  no  case  was  a  mummied  fruit 
found  which  showed  pink  spores  of  bitter  rot,  although  by  washing  with  a  little 
water  some  spores  were  found.  It  was  found  after  culturing  many  of  these  that 
the  hard,  very  compact  mummy  was  the  one  which  usually  contained  the  fungus 
in  the  living  condition  and  which  produced  the  spores.  The  mummied  fruits 
were  soaked  a  day  or  more  in  water  and  either  wrapped  in  moist  paper  or  put 
in  tight  wooden  boxes,  such  as  cigar  boxes,  and  frequently  sprayed  with  water. 
A  considerable  number  of  culture  experiments  were  made  and  the  majority  of 
the  hard  dried  mummies  produced  bitter  rot  spores.  A  number  of  infected  areas 
were  traced  to  such  mummied  fruits. 

Many  culture  experiments  were  also  made  with  mummied  fruits  gathered 
under  trees  on  the  ground.  Most  of  the  trees  were  known  to  have  had  bitter 
rot  the  previous  year.  These  mummies  came  from  various  Southern  Illinois 
orchards  and  were  cultured  as  those  taken  from  the  trees.  In  most  cases  they 
were  more  or  less  broken,  soft  and  attacked  by  saprophytic  fungi.  In  no  case 
was  there  any  development  of  the  bitter  rot  fungus  on  a  mummied  fruit  collected 
from  the  ground. 

On  November  22,  1906,  about  520  apples  infected  with  bitter  rot  in  various 
degrees,  which  had  been  recently  collected  under  trees  in  Richland  county,  Illi- 
nois, were  used  in  an  experiment,  the  purpose  of  which  was  to  test  the  effect 
on  the  vitality  of  the  fungus  of  outdoor  winter  conditions.  Of  these  apples  200 
were  put  on  the  ground  under  an  apple  tree  in  the  Horticultural  variety  orchard 
and  covered  over  with  a  wire  net  frame  ^-inch  mesh ;  200  were  enclosed  in  a 
similar  wire  net  frame,  and  placed  near  the  ground  on  2x4  inch  pieces.  In  both 
cases  the  apples  were  but  one  layer  deep.  The  remainder  of  the  apples  were 
suspended  from  a  tree  on  wires ;  some, — about  20, — were  susoended  individually 
and  the  others  .on  three  long  wires  stretched  from  limb  to  limb.  During  May, 
1907,  a  few  of  the  best  preserved  mummies  from  each  of  the  lots  mentioned 
above  were  cultured  in  the  laboratory,  but  no  evidence  was  obtained  that  the 
bitter  rot  fungus  was  alive  in  any  of  the  specimens.  In  June,  1907,  a  second  lot 
was  brought  in  and  given  cultural  treatment  with  the  same  result. 

None  of  the  mummied  fruits,  if  such  they  could  be  called,  were  in  the  hard, 
corky  condition  that  characterizes  the  typical  bitter  rot  mummy  which  naturally 
hangs  on  the  tree.  In  most  cases  saprophytic  fungi,  yfeasts,  and  bacteria  had 
attacked  the  only  partially  rotted  fruits,  and  as  a  result  left  the  decayed  apples 
in  a  more  or  less  soft,  (on  ground)  or  spongy,  (on  tree)  condition.  This  is  the 
same  condition  that  usually  prevails  in  bitter  rot  mummies  which  have  fallen 
in  summer  or  autumn  from  the  trees  and  lie  on  the  ground  over  winter. 

Experiment  12.  A  bitter  rot  canker  seven  inches  long  was  soaked  in  water 
one-half  hour  January  I,  1904.  It  had  been  cut  from  the  tree  in  Southern  Illinois 
late  in  November,  1903,  and  was  a  result  of  artificial  inoculation.  In  the  mean- 
time it  had  been  kept  in  a  cold  room  where  it  had  dried  but  little.  After  the 
soaking  it  was  suspended  over  a  steam  exhaust  pipe,  where  it  was  kept  warm 
and  moist.  On  January  14  many  pustules  of  bitter  rot  spores  were  exuding 
through  the  ruptured  places  in  the  bark.  The  canker  was  cut  transversely  into 
halves,  and  one-half  was  treated  with  a  solution  of  copper  sulfate,  six  pounds 
to  fifty  gallons  of  water.  The  two  halves  were  again  placed  in  the  green-house 
over  the  exhaust  steam.  On  February  2,  there  being  no  further  development,  the 
cankers  were  wrapped  in  moist  paper,  and  placed  in  a  tin  box.  After  ten  days 
both  pieces  of  the  canker  were  producing  pustules  of  spores  and  almost  as 
many  on  the  treated  as  on  the  untreated  half. 

Experiment  13.  On  February  2,  two  large  cankers  were  taken  from  the 
cold  room  and  soaked  in  water  over  night.  One  canker,  ten  inches  long,  pro- 
duced by  inoculation,  was  cut  transversely  into  halves  and  one-half  was  treated 
with  copper  sulfate  solution  of  the  same  strength  as  that  used  in  experiment  12. 


572  BULLETIN  No.  118.  [September, 

This  and  the  other  untreated  half  with  the  other  whole  canker  were  wrapped  in 
moist  paper  and  put  in  a  tin  box.  Six  days  later  all  were  producing  bitter  rot 
spores,  only  a  few,  however,  on  the  treated  half.  The  canker  cut  into  halves 
was  on  a  limb  seven-eighths  of  an  inch  in  diameter,  and  the  wood  was  darkened 
down  to  the  center.  When  the  examination  was  made  it  was  found  that  a  con- 
siderable amount  of  mycelium  was  coming  from  the  wood  of  the  cut  ends. 

Experiment  14.  A  small  canker,  about  three  inches  long,  was  cut  into 
halves.  One  piece  was  soaked  in  water  a  few  hours,  the  other  was  placed  on 
end  in  a  copper  sulfate  solution.  The  solution  was  two  inches  or  more  below 
the  canker  proper.  The  first  piece  was  wrapped  in  moist  paper,  and  after  three 
days  the  second  piece  was  removed  from  the  copper  sulfate  solution  and 
treated  as  the  first.  The  solution  had  been  taken  up  by  the  limb  and  was  oozing 
from  different  parts  of  the  canker.  Three  days  later,  March  8,  both  halves  of 
the  canker  were  producing  bitter  rot  spores. 

Experiment  15.  On  July  18,  the  two  halves  of  the  canker  used  in  experi- 
ment 13  were  put  to  soak  and  left  until  the  following  morning.  The  previously 
untreated  half  was  wrapped  in  moist  paper  and  placed  in  a  tin  box,  the  other 
half  was  sprayed  thoroughly  with  Cu  CO3  solution  of  the  strength  below :  Cop- 
per carbonate  \zV2  ounces,  ammonia  (weak)  75/2  pints,  water  50  gallons.  It  was 
then  wrapped  as  the  first  half.  Seven  days  later  both  pieces  were  producing 
bitter  rot  spores  in  about  equal  quantities. 

Experiment  16.  In  this  experiment  eight  cankers  were  used,  four  were  used 
as  checks  and  four  treated  with  Oregon  wash  made  up  according  to  the  follow- 
ing formula:  water  100  gallons,  sulfur  30  pounds,  copper  sulfate  2%  pounds, 
slacked  lime  30  pounds.  After  the  wash  had  dried  all  cankers  except  one  were 
soaked  six  hours  in  water  and  then  wrapped  in  moist  paper.  Five  days  later, 
April  2,  two  untreated  cankers  and  one  treated  had  developed  a  few  pustules  of 
spores.  April  7,  all  cankers  were  resoaked,  but  no  additional  spores  were  pro- 
duced. AprU  23,  they  were  soaked  over  night  again  and  five  days  later  all  of 
the  untreated  and  three  of  the  treated  cankers  were  producing  a  few  pustules 
of  spores. 

Experiment  17.  On  April  5,  the  two  halves  of  the  canker  used  in  experi- 
ments 13  and  15  were  soaked  in  water  and  the  previously  treated  half  was  coated 
with  Oregon  wash  and  with  the  other  put  into  the  moist  box.  Two  days  later 
there  was  no  development  of  spores,  and  the  cankers  were  again  soaked  in  water. 
April  n,  only  the  untreated  piece  was  producing  spores. 

WHEN  DOES  INFECTION  BEGIN? 

It  is  well  known  that  the  development  of  bitter  rot  of  apples  de- 
pends greatly  upon  climatic  conditions.  The  fungus  grows  well 
only  during  hot  weather  and  moisture  is  essential  to  the  germination 
of  the  spores.  Frequent  light  showers,  with  the  prevailing  temper- 
ature above  80°  Fahr.,  contribute  much  to  make  the  conditions  fay- 
orable  for  rapid  spread  of  the  malady  and  to  create  an  epidemic. 
Too  commonly  little  attention  is  given  the  matter  until  the  spotted 
fruit  shows  the  disease  is  already  well  under  way.  It  is  even  erro- 
neously claimed  by  some  investigators  that  the  fungus  is  so  sapro- 
phytic  in  character  that  it  only  grows  upon  fruit  that  has  nearly  or 
quite  reached  maturity  and  then  offers  little  resistance. 

Now  whatever  may  be  said  about  the  survival  over  winter,  it  is 
clearly  evident  that  the  abundant  production  of  spores  on  the  apples 
first  attacked  furnishes  the  principal  source  of  subsequent  infection. 
It  has  been  determined  that  under  favorable  circumstances  the  be- 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS  573 

ginning  of  a  new  crop  of  spores  may  follow  within  five  or  six  days 
after  the  seed-spores  are  placed  on  the  fruit,  and  even  in  a  shorter 
time  if  the  skin  is  mechanically  punctured.  As  innumerable  spores 
are  produced  upon  one  apple-spot,  abundant  infection  may  follow  its 
development.  The  date  when  this  latter  occurs  is,  therefore,  a  mat- 
ter demanding  careful  attention. 

The  earliest  record  made  by  ourselves  for  southern  Illinois  of 
the  appearance  in  the  field  of  the  disease  was  for  June  13,  1905, 
when  a  tree  of  Chenango  (Sherwood's  Favorite)  in  Richland 
county  was  found  badly  infected.  This  variety  is  among  the 
earliest  to  mature  its  fruit  and  at  the.  time  stated  the  apples  were 
nearly  full  grown.  The  rot-spots  in  some  cases  covered  one-half 
of  the  surface.  Many  of  the  spotted  fruits  had  fallen.  The  evi- 
dence, therefore,  that  at  least  thirteen  days  had  elapsed  since  the 
beginning  of  the  infection  seemed  conclusive  and  the  date  of  June  I 
may  be  put  down  for  this  beginning.  Other  observations  make  the 
middle  of  this  month  not  too  soon  to  anticipate  the  earliest  spots  on 
some  fruit  in  Illinois  between  38  and  39  degrees  of  north  latitude. 
If,  upon  this  date  only  a  very  few  apples  show  the  characteristic 
marks  of  the  disease,  there  may  be  enough  to  start  infection  in  great 
numbers  of  young  fruits  and  to  provide  the  way  for  serious  trouble 
later. 

FIELD  AND  LABORATORY  DATA 

On  July  2,  1903,  bitter  rot  was  found  in  two  different  orchards  at  Kell, 
Illinois.  In  one  case  Lowell  apple  was  infected,  in  the  other  Northern  Spy. 
The  size  and  appearance  of  the  affected  spots  indicated  that  the  first  outbreak 
was  not  less  than  ten  days  earlier.  The  Lowell  trees,  four  in  number,  bore  the 
infected  apples  mostly  on  the  lower  limbs  which  touched  the  ground  in  a  num- 
ber of  places.  The  trash  and  leaves  under  the  trees  were  more  or  less  moist  all 
the  time.  By  July  17  of  the  same  year  fully  fifty  percent  of  the  Ben  Davis  trees 
— a  large  number — in  the  orchard  containing  the  Lowell  trees  were  infected. 

The  first  report  of  bitter  rot  in  1904  came  from  Tamaroa,  111.,  about  July  15. 
One  Ben  Davis  tree  was  infected.  Bitter  rot  was  found  in  a  Kell,  111.,  orchard 
on  a  Northern  Spy  tree  on  July  20.  Some  of  the  apples  found  were  almost  half 
involved.  This  tree  was  the  same  Northern  Spy  tree  on  which  bitter  rot  was 
first  found  in  this  orchard  in  the  summer  of  1903. 

The  first  records  of  the  occurrence  of  bitter  rot  during  the  summer  of  1905 
were  made  on  June  13.  Many  bitter  rot  apples,  some  of  them  half  rotted,  were 
found  in  an  orchard  west  of  Olney,  111.,  on  four  Chenango  trees.  The  apples 
were  approaching  maturity  and  were  evidently  very  susceptible  to  this  disease. 
July  12,  the  rot  was  found  on  a  Northern  Spy  tree  at  Kell,  111.,  and  July  15  on 
two  Ben  Davis  trees  in  Olney,  111.,  orchard  No.  3,  one  infected  apple  on  each  tree. 

In  1906  the  first  report  of  bitter  rot  came  from  Olney  orchard  No.  3  on 
June  29.  July  26  it  was  reported  from  orchard  No.  i  at  Flora,  111.,  and  by  July 
27  seventeen  Ben  Davis  trees  in  Olney  orchard  No.  3  were  infected. 


574  BULLETIN  No.  118.  [September, 

THE  DISSEMINATION  OF  SPORES  BY  INSECTS 

The  mucillaginous  substance  exuded  with  the  spores  prevents 
them  in  this  state  from  carriage  as  dust  by  the  wind.  The  fact  that 
this  substance  together  with  the  spores  dries  into  a  hard  cake  seems 
further  to  prevent  wind  distribution.  While  adhesive,  the  spores 
may  stick  to  the  limbs  or  bodies  of  insects  and  thus  be  carried  about 
and  sometimes  deposited  on  the  surface  of  fruits.  That  this  actually 
occurs  was  early  shown  by  Clinton1,  and  both  before  and  since  his 
experiments  were  made,  this  method  of  distribution  has  been  as- 
sumed in  various  publications.  The  adhesive  character  of  the 
spores,  and  the  fact  that  so-called  pomace  flies  (Drosophila)  es- 
pecially are  everywhere  visitors  to  decaying  apples,  makes  the  sup- 
position almost  a  certainty  that  considerable  distribution  of  the 
spores  takes  place  by  this  means.  It  not  infrequently  happens  that 
the  first  affected  apples  on  a  tree  are  upon  the  lowest  limbs,  those 
perhaps  which  sweep  the  ground,  and  explanations  have  been  made 
that  these  slow-moving  flies  would,  after  their  visits  to  the  old  mum- 
mies lying  upon  the  ground,  most  likely  deposit  spores  on  these 
lowermost  fruits. 

We  shall  see  that  the  premises  here  are  not  sound,  whatever 
the  inference  may  be.  But  it  was  deemed  worth  while  further  to 
test  the  general  matter  by  experiments,  the  details  of  which  are 
reported  later  (see  data  following).  Clinton's  experiments  were 
repeated  with  apples  producing  spores  of  the  bitter  rot  fungus  in 
one  end  of  a  box  fourteen  inches  long  and  sound  apples  in  the  other 
end,  and  with  some  pomace  flies  shut  in  to  serve  as  distributing 
agents.  These  experiments  showed  results  similar  to  those  before 
reported.  The  sound  apples  soon  became  spotted  with  rot  evidently 
carried  by  the  flies.  On  making  microscopic  examinations  of  these 
flies  it  was  further  found  that  they  not  only  carry  spores  attached 
to  their  hairy  legs,  etc.,  but  that  they  feed  upon  them.  The  spores 
still  whole  and  apparently  sound  can  be  easily  seen  through  the  semi- 
transparent  bodies  in  the  intestines,  and  in  considerable  numbers. 
It  was  not  satisfactorily  made  out  that  any  of  these  spores  were 
actually  voided  in  a  condition  permitting  germination,  but  fruit  in- 
oculations with  crushed  flies  were  often  followed  by  the  development 
of  the  disease.  At  all  events  the  fact  that  the  flies  eat  the  spores 
strengthens  the  supposition  that  the  insects  play  some  role  in  the 
spore  distribution  in  nature,  since  they  must  be  attracted  to  infected 
fruits  when  spores  are  exuding  and  also  to  those  upon  whose  sur- 

I.  Clinton,  G.  P.,  Apple  Rots  in  Illinois.    Bui.  111.  Ag,-  E*p.  Sta.  69:197, 


1907.}        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  575 

faces  spore-masses  previously  produced  have  dried  and  remain  some- 
what adhesively  attached.  It  has  not  been  shown  that  other  insects 
are  agents  in  a  similar  way  in  this  distribution,  and  from  what  is 
now  known,  it  is  not  at  all  likely  that  any  insects  are  largely  instru- 
mental in  aiding  infection  through  punctures  of  the  epidermis  of 
growing  fruits,  or  of  the  bark  of  susceptible  limbs.  On  the  fruits 
the  spores  do  not  need  such  aid  when  the  weather  conditions  favor 
their  germination.  In  this  case  all  that  is  necessary  is  that  the 
spores  while  still  possessing  vitality  shall  be  carried  to  and  lodged 
upon  the  unbroken  surface  of  the  apples,  although  punctures  such  as 
may  be  made  with  a  needle  facilitate  the  fungous  atttack. 

Upon  the  whole,  it  seems  pretty  certain  that  in  the  orchard,  in- 
sects have  small  part  in  the  dissemination  of  the  disease.  The  little 
flies  mentioned  do  sometimes  carry  the  spores  and  may  sometimes 
deposit  them  on  the  surfaces  of  fresh  fruits  in  such  way  that  new 
infection  results,  but  there  is  little  evidence  in  support  of  this  from 
direct  observation  or  from  anything  really  known  which  lends  sug- 
gestiveness  to  the  proposition.  The  greater  infection  sometimes 
observed  upon  the  lower  limbs  must  surely  be  explained  in  some 
other  way,  because  (to  be  shown  later)  the  infection  does  not  arise 
from  the  ground.  Insect  agency  need  not  now  be  considered  at  all 
to  explain  satisfactorily  the  distribution  of  the  disease  in  an  orchard. 

FIELD  AND  LABORATORY  DATA,  1903 

Experiment  I.  Twenty  Drosophila  flies  collected  about  bitter  rot  apples  were 
crushed  and  examined  one  at  a  time*  under  the  microscope  for  bitter  rot  spores, 
and  fourteen  of  the  twenty  contained  such  spores  in  the  alimentary  tract.  Twenty 
inoculations  were  made  with  these  crushed  flies,  by  inserting  them  under  the 
skin  of  apples  and  six  of  them  developed  bitter  rot. 

Experiment  2.  At  5  p.m.,  July  10,  twelve  flies  were  collected  about  infected 
apples  and  three  placed  in  each  of  four  vials.  At  the  end  of  fifteen  hours,  July 
ii,  8  a.m.,  the  flies  of  vial  Nos.  i  and  2  were  examined  and  two  in  No.  i  were 
dead.  Only  the  living  fly  contained  bitter  rot  spores.  All  three  flies  in  vial 
No.  2  were  living  and  only  one  contained  spores  of  bitter  rot.  A  little  water 
was  added  to  each  vial  and  after  shaking  well  four  apples  were  inoculated  with 
the  water  from  each.  Three  of  the  inoculations  from  vial  No.  i  developed  bitter 
rot.  At  the  end  of  twenty-two  hours  the  flies  of  vial  Nos.  3  and  4  were  exam- 
ined. All  flies  were  dead  and  all  three  flies  of  vial  No.  3  and  one  of  No.  4 
contained  bitter  rot  spores.  Inoculations  were  made  with  both  the  flies  and 
the  wash  water  from  each  vial.  One  inoculation,  a  fly  from  vial  No.  3  produced 
bitter  rot. 

Experiment  3.  In  one  end  of  a  box  fourteen  inches  long,  ten  inches  wide, 
and  eight  inches  high  were  placed  several  bitter  rot  apples  producing  many  spores. 
In  the  other  end  were  six  sound  apples,  part  of  which  were  punctured  in  many 
places  with  a  fine  needle.  After  a  number  of  flies  had  entered  the  box  a  glass 
plate  was  placed  over  the  top.  By  varying  the  position  of  the  box  with  refer- 
ence to  the  light  causing  the  shadow  to  fall  on  one  then  in  other  end  of  the  box, 
the  flies  being  positively  heliotropic  (going  toward  the  light)  could  be  kept  for  a 
time  on  or  about  the  infected  apples  then  changed,  with  somewhat  less  success, 
to  the  sound  ones.  After  six  days  the  sound  apples  were  removed  to  moist 


576  BULLETIN  No.  118.  [September, 

conditions  at  room  temperature.  Four  of  the  six  apples  developed  bitter  rot. 
On  July  24,  more  sound  apples  were  placed  in  the  box  and  at  the  end  of  seven 
days  removed  to  a  moist  chamber  where  two  of  the  six  apples  developed  bitter 
rot.  A  third  set  was  left  in  the  box  five  days  then  removed  as  the  others.  One 
apple  became  infected. 

Experiment  4.  A  microscopic  object  slide  smeared  with  glycerine  was  placed 
on  a  plate  with  a  number  of  bitter  rot  apples  about  which  were  many  Droso- 
phila  flies.  After  three  days  the  glycerine  was  washed  off  with  a  little  water  into 
a  small  dish  and  examined.  Quite  a  number  of  bitter  rot  spores  were  present 
in  the  water.  Twenty-four  hours  later  a  number  of  the  spores  had  germinated. 
July  14,  this  test  was  repeated  with  five  slides  instead  of  one.  At  the  end  of 
three  days  the  slides  were  washed  and  an  examination  showed  that  spores  were 
on  all  of  the  slides.  Some  of  these  spores  germinated  later.  Again  the  test  was 
repeated  on  July  21,  and  spores  were  found  on  each  slide. 

DISTRIBUTION  BY  WATER 

The  cohering  spore-masses  dissolve  immediately  when  placed  in 
water,  whether  or  not  drying  has  previously  taken  place.  The 
agglutinating  substance  is  readily  soluble  in  rain  or  other  water.  It 
is  easy,  therefore,  for  the  spores  to  be  washed  down  from  an  in- 
fecting source  to  the  lower  parts  of  a  tree  by  rain  water.  All  ob- 
servations, confirmed  by  actual  tests,  show  that  infection  is  spread 
in  this  way,  and  much  more  by  drizzling  showers  than  by  heavy 
rains.  The  spores  are  washed  down  in  both  cases,  but  in  the  lat- 
ter they  have  little  chance  to  remain  on  any  exposed  surfaces — they 
are  washed  entirely  off  and  seem  to  fail  in  getting  back.  The  well- 
known  cone  of  infection  on  the  limbs  of  a  tree  with  a  canker  or 
earlier  affected  apple  at  its  apex,  is  thus  best  brought  about  by  very 
moderate  showers  or  even  by  dew,  if  that  is  heavy  enough  to  cause 
dripping,  and  this  is  no  doubt  why  such  well  marked  areas  of  infec- 
tion are  sometimes  so  much  easier  observed  than  at  other  times ;  in 
some  seasons,  perhaps,  than  in  other  seasons.  They  were  exceed- 
ingly common  and  well  marked  the  year  when  the  cankers  were 
first  discovered  (1902),  but  they  had  often  been  observed  and  de- 
scribed before  that  date. 

DISTRIBUTION  BY  WIND 

That  the  spores  are  actually  washed  down  in  trees  by  rain  was 
early  shown  from  experimental  tests  by  Hasselbring  (1902),  and 
the  fact  has  been  abundantly  verified  by  similar  experiments  since 
that  time.  It  is  also  clear  enough  that  rain  with  heavy  winds  may 
sometimes  carry  the  spores  from  tree  to  tree  with  droplets  and 
splashes  of  water,  because  the  latter  are  certainly  so  carried.  But 
again  these  conditions  are  not  the  most  favorable  for  the  lodgment 
of  spores,  on  the  surfaces  of  fruits,  and  the  spread  of  the  disease  in 
orchards  still  seemed  mysterious.  There  is  undoubtedly  much  dif- 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL" INVESTIGATIONS.  577 

ference  during  different  seasons  as  to  this  dissemination  in  the 
orchard.  Sometimes  a  thoroughly  infected  tree  stands  alone  with  no 
others  harmed  even  though  these  others  are  of  the  same  variety  and 
evidently  equally  susceptible;  at  other  times,  doubtless  more  often, 
the  neighboring-  trees  in  gradation  by  proximity  show  the  effects 
of  the  situation.  It  may  be  easy  to  surmise  why  such  difference  ap- 
pears, but  we  have  no  other  exact  published  data  to  quote,  and 
nothing  to  offer  except  what  follows.  Since  the  discovery  of  the 
limb-cankers  it  is  well  understood  why  some  one  tree  continues  to 
be  infected  year  after  year,  but  why  there  should  be  so  much  dif- 
ference in  the  spread  t>f  infection  from  such  a  tree  has  been  the 
puzzle. 

It  has  everywhere  been  assumed  in  our  own  and  other  publica- 
tions that  the  wind  can  play  little  part  in  the  dissemination  of  the 
spores,  because  of  the  mucillage  in  which  they  are  embedded  as  they 
issue  from  the  spore-pustules,  and  the  hardened  crust  this  forms 
when  dried.  It  is  indeed  impossible  for  air  currents  to  move  the 
spores  from  surfaces  to  which  they  are  glued  when  the  attachment 
is  at  its  best.  When  the  substance  with  the  spores  is  of  the  proper 
consistency  to  flatten  down,  as  would  a  droplet  of  thick  syrup,  into 
an  even,  convex,  closely  adherent  body — and  this  is  frequently  the 
case — surely  it  cannot  be  broken  in  fragments  or  become  detached 
by  the  action  of  the  wind  unaided  by  anything  else.  Whenever  the 
spore-mass  is  in  the  condition  of  serviceable  paste  or  when  like 
hardened  gum,  removal  by  wind  cannot  occur. 

It  is  a  fact,  however,  that  the  consistency  of  the  spore-masses 
varies  much.  When  the  fungus  is  in  very  active  development  and 
the  air  is  fairly  moist,  the  issue  from  the  pustules  is  in  the  shape  of 
slender  threads  which  become  variously  curved  or  coiled  (PI.  V., 
Fig.  i ) .  Bits  of  these  threads  may  be  easily  separated  and  carried 
away  by  air  in  rapid  motion.  Under  certain  atmospheric  and  per- 
haps other  conditions  the  spore-masses  have  little  viscidity;  they 
readily  crumble,  and  bits  containing  a  considerable  number  of  spores 
and  particles  of  the  spore-masses  may  thus  be  separated  and  then 
can  be  removed  and  carried  off  in  a  stiff  breeze.  Further  there  is 
more  or  less  rubbing  of  the  surface  of  apples  on  the  tree  by  the 
leaves  and  branches  through  the  movements  caused  by  the  wind, 
and  particles  of  the  spore-masses  may  thus  be  separated  and  then 
borne  away  in  the  air.  The  conditions  are  really  not  such  as  must 
necessarily  prevent  dissemination  of  spores  by  the  air  in  motion. 
Practical  experiments  show  that  they  are  so  (.".  tributed  and  suf- 
ficiently to  explain  phenomena  not  heretofore  understandable. 


578  BULLETIN  No.  118. 

Whethers  the  dust-like  particles  have  one  or  numerous  more  or 
less  coherent  spores  in  them  may  not  be  important;  so  long-  as 
they  are  carried  in  any  shape  while  retaining  their  vitality,  infection 
at  a  distance  must  be  possible,  and  under  favoring  conditions  prob- 
able. 

In  order  to  test  the  matter  experimentally,  glass  slips  3  by  i  inch, 
used  in  ordinary  work  with  the  microscope,  smeared  with  glycerine, 
were  placed  'from  14  to  24  inches  from  infected  apples  having 
spores  issuing  from  pustules.  Movements  of  air  were  caused  to 
pass  the  rotting  apples  towards  the  glass  slips,  by  means  of  a  small 
bicycle  pump,  or  at  other  times  the  natural  breeze  through  an  open 
window  or  in  the  field  was  utilized  for  the  purpose  (see  data  fol- 
lowing, Expts.  1-9).  In  numerous  instances  microscopical  examina- 
tions of  the  smeared  slides  showed  the  presence  of  spores  of  the  bit- 
ter rot  fungus,  either  singly  or  in  pellets.  Further  to  test  this  in  the 
orchard,  a  tin  funnel  was  constructed  16  inches  across  its  wide  end 
and  2  inches  at  the  exit.  At  the  latter  tincups — with  end  of  fine  wire 
screen — filled  with  glass  wool,  moistened  with  a  mixture  of  alcohol 
and  glycerine,  were  made  to  fit  so  as  to  be  readily  removable.  The 
funnel  was  fixed  upon  a  7-foot  stake  which  could  be  thrust  into  the 
ground  and  was  then  used  in  various  positions  in  the  orchard  with 
the  open  mouth  to  the  wind.  After  exposure,  the  glass  wool  was* 
washed  in  a  little  water  and  this  was  then  examined  for  spores.  In 
no  case  as  tried  were  all  the  conditions  favorable  and  but  few  spores 
of  this  fungus  were  ever  found  in  the  wash  water,  but  there  were 
enough  to  show  again  that  they  are  sometimes  distributed  by  the 
wind.  Undoubtedly  further  tests  of  this  kind  would  be  more  con- 
vincing (see  data  following,  Expts.  10-13). 

It  was  shown  that  spores  which  had  been  carried  by  the  wind 
were  capable  of  germination  by  direct  culture  and  microscopic  tests. 
There  can  be  no  doubt  now  but  that  infection  spreads  to  some  ex- 
tent from  tree  to  tree  in  an  orchard,  and  possibly  though  to  a  much 
less  extent,  from  orchard  to  orchard,  by  means  of  wind-carried 
spores  derived  either  from  the  limb-cankers  or  much  more  likely, 
because  of  the  greater  production,  from  diseased  fruit.  If  this 
method  of  distribution  in  a  given  tree  is  comparatively  ineffective, 
and  it  is  sometimes  shown  to  be  so  by  the  cone-shaped  area  of  spot- 
ted fruit  under  a  single  spore-producing  body,  it  nevertheless  offers 
explanation  of  observed  facts  which  have  been  otherwise  puzzling, 
and  it  emphasizes  anew  the  prime  importance  of  destroying  the  con- 
tagion at  its  source.  Any  diseased  tree  is  a  menace  to  others  nearby 
and  to  some  degree  to  those  widely  distant  whether  or  not  insects 


1907.]         BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS. 


579 


are  actively  carrying  the  spores.  Whether  or  not  the  spores  may 
be  subject  to  wind-dissemination  depends  much  upon  the  conditions 
under  which  they  are  produced,  and  this  again  offers  explanations 
for  observed  peculiarities  in  this  respect.  They  may  at  one  time  be 
widely  distributed  and  may  not  be  movable  by  wind  at  all  at  some 
other  time,  owing  to  the  state  and  peculiarities  of  exudation  from 
the  producing  pustules,  and  to  the  peculiarities  of  the  weather. 

Much  importance  is  placed  upon  these  experiments  and  their  re- 
sults. They  not  only  clear  up  difficulties  heretofore  existing  in 
studies  of  geographical  progress  of  the  disease,  but  they  emphasize 
anew  the  importance  of  thorough  work  in  exterminating  the  con- 
tagion when  first  discovered  and  of  keeping  a  sharp  outlook  for  it 
during  the  season  of  its  development.  Any  stamping  out  process  is 
futile  unless  absolute  extermination  is  accomplished.  The  main 
service  of  these  studies  is  to  tell  when  and  where  to  strike  most  ef- 
fectively and  most  economically.  In  this  there  is  evident  need  of 
cooperation  when  different  owners  or  managers  have  adjoining  or 
nearly  adjoining  orchards,  and  there  may  be  need  of  legislation 
making  effort  compulsory. 

FIELD  AND  LABORATORY  DATA 

Experiment  I.  Three  wet  microscopic  object  slides  were  placed  on  end  four- 
teen inches  from  four  infected  apples  bearing  exuding  pustules  of  bitter  rot 
spores.  After  passing  a  current  of  air  from  a  small  bicycle  pump  over  the 
infected  apples  toward  the  glass  slides  for  a  few  seconds,  the  slides  were  exam- 
ined and  bitter  rot  spores  were  found  on  each. 

Experiment  2.  Four  wet  glass  slides  were  placed  eighteen  inches  from  an 
infected  apple  bearing  many  tendrils  of  bitter  rot  spores.  The  air  current  from 
the  bicycle  pump  was  passed  over  the  infected  apple  in  the  direction  of  the  slides 
a  few  seconds.  An  examination  of  the  slides  showed  that  not  only  single  spores, 
but  small  masses  had  been  blown  to  the  slides. 

Experiment  3.  A  wooden  box  was  constructed  8  inches  wide,  8  inches  deep, 
and  24  inches  long  with  one  removable  side  and  a  small  hole  in  one  end.  By 
means  of  small  nails,  driven  through  the  box  sound  apples  were  arranged  on 
the  inside  walls  of  one  end  of  the  box.  On  the  bottom  of  the  opposite  end  of  the 
box  were  placed  four  apples  bearing  many  pustules  of  bitter  rot  spores.  By 
means  of  the  small  bicycle  pump  a  current  of  air  was  passed  through  the  hole  in 
the  box  and  over  the  infected  apples  toward  the  sound  ones.  Along  with  the 
sound  apples  was  a  wet  slide  on  which,  after  passing  the  air  current,  one  hun- 
dred fifteen  bitter  rot  spores  were  counted.  Two  of  the  six  sound  apples  used 
became  infected  with  bitter  rot. 

Experiment  4.  Five  apples  were  punctured  with  a  fine  needle  and  placed  in 
one  end  of  the  wooden  box  used  in  experiment  3  and  that  experiment  was  re- 
peated. After  three  days  several  spots  of  bitter  rot  on  three  apples  had  de-> 
veloped. 

Experiment  5.  Thinking  that  perhaps  the  current  of  air  from  the  bicycle 
pump  was  stronger  than  would  ordinarily  be  met  with  in  the  orchard,  some  tests 
were  made  with  the  natural  breeze.  An  apple  bearing  many  tendrils  of  bitter  rot 
spores  was  held  before  the  open  window  permitting  the  incoming  breeze  to  pass 
over  it  and  onto  a  wet  slide  some  eighteen  inches  behind.  This  test  was  re- 
peated three  times  with  three  different  apples,  and  in  each  case  bitter  rot  spores 
were  found  on  the  slide.  The  same  test  was  tried,  but  with  three  dry  instead  of 
one  wet  slide.  Bilter  rot  spores  were  found  on  two  of  the  slides. 


580  BULLETIN  No.  118.  [September, 

Experiment  6.  In  this  test  the  breeze  that  passed  into  the  open  window  was 
quite  strong.  It  was  permitted  to  pass  over  an  infected  apple  bearing  spores  and 
onto  a  wet  object  slide.  This  was  repeated  several  times  and  in  most  cases 
spores  were  found  on  the  slide. 

Experiment  7.  Six  infected  apples  bearing  some  pustules  of  bitter  rot  spores 
were  taken  from  a  Northern  Spy  tree  and  brought  into  the  laboratory  for  test- 
ing. The  spots  on  the  apples  were  large  and  the  spore-masses  somewhat  dried 
down.  Five  of  the  apples  were  subjected  to  currents  of  air  from  both  the  bicycle 
pump  and  the  open  window.  In  every  case  spores  were  found  on  the  wet  ob- 
ject slides. 

Experiment  8.  Two  apples  punctured  in  many  places  with  a  needle  were 
moistened  and  a  current  of  air  from  the  bicycle  pump  passed  over  infected  ap- 
ples toward  them.  At  the  end  of  three  days  the  two  apples  showed  a  total  of 
38  spots  of  bitter  rot. 

Experiment  9.  By  means  of  the  air  current  from  the  bicycle  pump  bitter 
rot  spores  were  blown  from  an  infected  apple  into  a  small  dish  containing  weak 
beef  broth.  Within  five  hours  twenty-five  percent  of  the  spores  had  germinated 
and  at  the  end  of  twenty-four  hours  seventy-five  percent  showed  activity. 

Experiment  10.  In  order  to  test  whether  the  wind  that  passed  through  the 
trees  and  over  the  infected  apples  in  the  orchard  carried  bitter  rot  spores,  a  num- 
ber of  experiments  were  made  with  a  large  tin  funnel.  This  funnel  was  sixteen 
inches  in  diameter  of  mouth,  and  sixteen  inches  in  length,  and  to  the  small  end 
were  attached  tin  cups  two  inches  in  diameter  and  four  inches  long.  Over 
the  outer  end  of  the  cup  was  fastened  a  piece  of  fine  wire  netting  which  held  in 
place  a  small  amount  of  glass  wool.  After  saturating  the  glass  wool  with  a  mix- 
ture of  alcohol  and  glycerine  and  adjusting  the  cup,  the  funnel  supported  on  a 
seven-foot  pole  was  set  up  facing  the  wind  and  a  tree  infected  with  bitter  rot. 
This  tree,  a  Northern  Spy,  had  but  a  few  bitter  rot  apples  on  it.  After  two  days 
the  cup  was  removed  and  the  glass  wool  washed  with  water.  An  examination  of 
the  water  showed  the  presence  of  many  pollen  grains,  some  spores  of  several 
kinds,  but  none  of  bitter  rot. 

After  the  funnel  had  remained  before  a  second  tree  two  days,  an  examina- 
tion revealed  one  bitter  rot  spore  in  the  wash  water.  Showers  during  the  inter- 
val that  the  funnel  was  up  made  the  spores  unsuitable  for  wind  dissemination. 

Experiment  n.  The  large  funnel  was  taken  to  Kell  orchard  No.  I,  where 
there  were  more  trees  infected  with  the  rot  and  set  up  before  a  Ben  Davis  tree 
bearing  a  few  infected  apples.  At  the  end  of  three  days  no  bitter  rot  spores 
were  discovered  in  the  glass  wool. 

Experiment  12.  The  funnel  was  set  up  in  the  open,  facing  the  wind,  and 
twelve  inches  before  it  were  suspended  a  number  of  bitter  rot  apples  bearing 
many  pustules  of  spores.  After  two  days  no  bitter  rot  spores  were  found.  New 
apples  were  placed  before  the  funnel  and  after  two  days  more  an  examination 
showed  the.  presence  of  bitter  rot  spores  in  the  wash  water.  During  the  last 
two  days  the  wind  was  quite  mild.  After  leaving  a  second,  cup  on  the  funnel  as 
it  stood  in  the  last  test  for  twenty-four  hours,  three  washings  of  the  glass  wool 
were  made  and  examined.  Spores  were  found  in  all  three,  but  the  most  in  the 
first  wasK  water.  Two  days  later  a  third  cup  was  examined  and  many  bitter  rot 
spores  were  found  suspended  near  the  bottom  of  the  dish  in  the  mixture  of 
glycerine  and  water.  It  is  quite  probable  that  in  former  observations  spores 
were  overlooked,  thinking  at  the  time  that  they  all  settled  to  the  bottom  of 
the  dish. 

Experiment  13.  The  apples  used  in  the  last  test  of  experiment  12  were  re- 
placed by  old  apples,  almost  mummies,  but  bearing  many  dried  pustules  of 
spores.  At  the  end  of  twenty-four  hours  the  glass  wool  was  washed  and  the 
water  examined.  A  few  bitter  rot  spores  were  found  in  each  of  the  first  three 
washings. 

On  July  27,  the  above  apples  were  replaced  by  newly  infected  apples  bearing 
many  exuding  tendrils  of  spores.  After  two  days  a  cup  from  the  funnel  was 
examined  and  a  few  spores  were  found,  more  in  the  first  washing  than  in 
the  second  and  third.  Heavy  dews  rendered  the  spores  unfit  for  wind  dissem- 
ination. A  new  lot  of  apples  was  placed  before  the  funnel  and  after  three  days 
the  cup  was  examined.  Very  few  bitter  rot  spores  were  found. 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  581 

TPIE  ORIGIN  OF  EPIDEMICS 

It  is  now  possible  to  undertake  an  answer  to  the  question : 
"How  does  the  disease  start  in  any  season?"  or  "What  is  the  sea- 
sonal beginning  of  an  epidemic?"  Here  is  the  problem  upon  which 
these  investigations  were  hoped  especially  to  throw  some  light.  It 
has  been  well  shown  elsewhere  that  by  proper  spraying  the  greater 
proportion  of  loss  can  be  prevented.  This  is  upon  the  understand- 
ing that  the  spray  material  protects  the  fruit  from  the  spores  of  the 
fungus  which  are  deposited  upon  their  surfaces.  Is  there  any  way 
to  strike  more  nearly  at  the  root  of  things  ?  Can  the  formation  and 
dissemination  of  these  spores  be  prevented?  May  an  epidemic  be 
controlled  by  heading  it  off  entirely? 

We  understand  fully  that  neither  this  nor  any  other  disease  of 
transmissible  character  affecting  animals  or  plants  can  occur  with- 
out the  presence  and  successful  action  of  a  definite  or  specific  para- 
site which  is  the  active  agent  of  the  trouble.  There  very  certainly 
can  be  no  bitter  rot  disease  of  apples  without  the  bitter  rot  fungus. 
The  contagion  cannot  start  at  the  beginning  of  a  season  without  the 
successful  passing  of  the  winter  by  the  agent  constituting  the  con- 
tagion. This  latter  must  retain  its  vitality  and  must  start  again  in 
its  own  growth  before  any  new  effect  is  possible  on  the  tree  or  fruit. 

We  know  that  there  are  what  seem  to  be  inscrutible  differences 
in  outbreaks  of  the  disease.  Though  history  in  this  case  more  com- 
monly repeats  itself  year  after  year  in  different  orchards,  it  is  at 
times  decidedly  variant.  Without  apparent  reason  one  orchard  of 
a  given  number  may  suffer  severely  in  comparison  with  others  one 
season,  and  escape  the  next  while  another  bears  the  chief  burden  of 
injury.  Effects  follow  causes.  If  such  things  are  mysterious,  it  is 
only  because  we  are  ignorant  of  ascertainable  facts  not  because  the 
matter  is  beyond  our  full  comprehension.  What  we  do  not  know 
is  no  credit  to  us ;  the  more  we  can  find  out  the  better  fixed  we  shall 
be  to  understand  whatever  remains  to  be  found  out.  It  is  in  this 
spirit  that  work  upon  the  special  problem  in  hand  has  been  under- 
taken and  prosecuted.  Beginning  with  the  well  grounded  idea  that 
all  mystery  connected  with  the  seasonal  outbreaks  of  the  disease 
may  become  real  knowledge,  we  have  undertaken  to  bring  this  to 
pass.  Fighting  in  the  dark  is  unprofitable  if  by  any  means  we  can 
turn  on  the  light ;  the  latter  is  our  task. 

The  discovery  of  the  limb-cankers  was  a  notable  event.  Its  im- 
portance has  never  been  exaggerated.  The  facts  announced  have 
remained  facts  and  the  accounts  as  published  are  still  true.  But  the 
cankers  do  not  tell  the  whole  story  concerning  the  seasonal  origin 


582  BULLETIN  No.  118.  [September, 

of  epidemics.  As  herein  before  stated  there  are  great  seasonal  and 
apparently  geographical  variations  in  the  formation  of  cankers  and 
in  relation  to  their  existence  and  numbers  compared  with  the  extent 
of  infection.  There  is  something  else  to  be  taken  in  account  besides 
peculiarities  of  weather  and  the  presence  of  the  living  fungus  in 
localized  spots  on  the  limbs,  though  abundant  evidence  exists  that 
in  many  cases  these  cankers  do  constitute  the  source  from  which  the 
malady  starts  and  are  themselves  in  these  cases  sufficient  explana- 
tion of  all  that  follows.  It  is  as  important  today  as  it  was  deemed 
to  be  when  directions  were  first  made  in  regard  to  the  process,  that 
these  infected  limbs  should  be  carefully  removed  or  in  some  way 
rendered  sterile.  There  is  really  nothing  now  of  importance  to  add 
to  the  early  publications,  as  there  is  nothing  to  retract  or  modify, 
concerning  the  bitter  rot  cankers  and  their  relation  to  the  spread  of 
the  disease,  except  that  we  know  more  about  the  difficulties  attend- 
ing their  complete  removal  and  of  killing  the  fungus  by  external 
washes. 

But  fuller  recognition  exists  that  outbreaks  of  the  disease  must 
be  sometimes  attributed  to  something  else,  to  some  other  means 
of  passing  the  winter  on  the  part  of  the  parasite.  Renewed  atten- 
tion has  been  given  to  the  mummies.  Cone-shaped  areas  of  infec- 
tion on  trees  have  been  traced  to  one  of  these  old  shriveled  apples 
hanging  above,  in  numerous  instances.  Such  old  fruits  have  also  in 
numerous  instances  produced  an  abundance  of  spore-masses  when 
brought  from  the  trees  in  May  or  later  into  the  laboratory  and  sub- 
mitted to  conditions  suitable  for  the  renewal  of  activity  of  the 
fungus  (PI.  VIII.,  Fig.  2).  The  case  is  as  well  made  out  that  an 
outbreak  of  bitter  rot  may  be  due  to  old  mummies  as  it  has  been 
in  regard  to  the  cankers,  and  sometimes  and  in  some  places  this 
seems  to  be  the  more  common  occurrence. 

However,  it  was  soon  learned  that  mummies,  undoubtedly  orig- 
inated by  the  bitter  rot  fungus  the  year  before,  were  not  all  fertile. 
The  fungus  does  not  always  remain  alive  over  winter  in  these  old 
infected  apples.  In  this  respect  there  is  certainly  a  marked  differ- 
ence between  them  and  the  cankers.  In  the  latter  there  is  appar- 
ently no  condition  or  circumstance  when  the  fungus  fails  to  survive 
at  least  one  winter,  and  it  may  do  so  for  two  or  even  more  seasons 
in  their  natural  positions.  Why  the  relative  unreliability  of  the 
mummies  ? 

Studies  upon  the  cankers  have  shown  that  the  bitter  rot  fungus 
usually  has  in  this  infection  the  field  to  itself.  No  other  fungous 
parasite  or  saprophyte  commonly  interferes,  although  black  rot, 


1907.]        BITTER  ROT  OP  APPLES,  BOTANICAL  INVESTIGATIONS.  583 

Sph&ropsis  malorum,  is  sometimes  associated  in  the  same  canker, 
usually  in  Illinois  as  a  later  intruder.  While  the  fungus  of  bitter 
rot  has  a  remarkably  preservative  effect  upon  the  cell-walls  of  apple 
fruits,  causing  the  substance  to  assume  a  corky  character,  the  inva- 
sion of  bacteria,  yeasts,  and  saprophytic  fungi  of  many  kinds  is 
more  than  not  liable  to  happen,  as  the  fruits  remain  exposed  to  the 
weather  out  of  doors.  With  sufficient  moisture  these  saprophytes 
are  certain  to  develop  and  in  their  development  they  destroy  the 
dormant  parasite.  They,  or  some  of  them,  thrive  at  much  lower 
temperatures  than  does  the  bitter  rot  plant,  and  thus  during  the  win- 
ter and  spring  they  have  very  decidedly  the  advantage.  The  old 
fruits  lose  their  firm,  cork-like  consistence  and  become  soft  or  fri- 
able. In  this  state  they  lose  or  have  lost  their  infective  character- 
istics. The  bitter  rot  fungus  is  dead  whenever  the  old  fruit  sub- 
stance becomes  soft  or  easily  broken,  and  it  has  left  behind  no  spores 
capable  of  renewing  its  existence. 

Let  us  see  now  under  what  circumstances  in  nature  the  fungus 
is  likely  to  retain  its  vitality  in  the  old  apples  upon  which  it  de- 
veloped the  preceding  year.  The  date  and  conditions  of  this  de- 
velopment will  evidently  have  some  deciding  influence.  After  the 
fungus  has  gained  entrance  to  the  tissues  of  growing  fruits,  its  own 
growth  proceeds  without  much  reference  to  outside  moisture  con- 
ditions. If  the  atmosphere  continues  dry  other  soft  rots  are  not  so 
likely  to  follow  before  the  entire  fruit  is  involved  in  the  action  of 
the  parasite.  This  latter  undoubtedly  has  its  own  way  better  without 
competition  of  other  fungi  when  the  fruit  is  attacked  while  com- 
paratively young.  The  texture  assumes  the  cork-like  character  de- 
scribed above  and  if  the  shrunken  fruit  is  now  little  exposed  to  soft 
rot  agents,  the  fungus  easily  survives.  If  on  the  other  hand,  the 
bitter  rot  infection  is  late  in  the  season,  when  the  maturity  of  the 
fruit  and  the  external  conditions  are  more  favorable  for  saprophytic 
growth,  the  less  chance  there  must  be  that  the  bitter  rot  fungus  can 
continue  alive.  There  must  also  be  the  possibility  of  decisive  dif- 
ference as  to  whether  after  the  formation  of  the  mummy  most  suit- 
able for  the  perpetuation  of  the  fungus,  the  old  fruit  continues  to 
hang  upon  the  tree,  or  drops  to  the  ground.  We  know  that  drying 
does  not  kill  the  parasitic  mycelium;  it  does  tend  to  prevent  the 
action  of  soft-rot  fungi.  The  mummy  hanging  over  winter  on  the 
tree  is  more  likely  to  remain  dry  and  hard,  those  on  the  ground  to 
be  moist  and  to  become  the  habitat  of  numerous  kinds  of  fungi, — 
fermentation  and  decay  producers.  The  bitter  rot  fungus  should 
then  be  much  more  likely  to  live  over  winter  in  the  mummies  which 


584  BULLETIN  No.  118.  [September, 

remain  attached  to  the  fruit-spurs  than  in  those  that  lie  upon  the 
ground. 

To  determine  the  truth  in  this  matter,  extended  studies  were 
made  on  old  apples  in  the  field  and  in  the  laboratory,  and  the  results 
were  abundantly  conclusive.  Sometimes  those  remaining  on  the 
trees  until  May,  or  June,  or  later,  of  the  succeeding  year  show  grad- 
ual breaking  down  with  other  rots,  but  this  is  somewhat  uncommon. 
When  it  does  occur  the  old  fruits  soon  become  easily  detached  from 
the  limb,  while  those  continuing  firmly  adherent  are  the  ones  in 
which  the  bitter  rot  fungus  is  more  often  found  in  a  living  state. 
Out  of  hundreds  of  specimens  (certainly  known  to  have  been  origi- 
nally affected  with  bitter  rot)  remaining  on  the  ground  over  winter 
and  picked  up  after  May  i,  during  three  successive  seasons,  none 
have  produced  spores  of  the  fungus  when  placed  in  moist  chambers 
and  kept  under  conditions  favoring  the  process,  or  have  given  other 
indications  of  the  vitality  of  this  fungus.  Numerous  specimens, 
again  numbering  in  the  hundreds,  spotted  with  the  rot  collected  at 
the  time  of  the  apple  harvest  and  placed  on  the  ground  soon  after- 
ward in  various  situations  have  always  shown  decay  the  next  spring 
and  have  failed  to  give  any  indications  of  the  vitality  of  the  myce- 
lium of  Glceosporium.  Plate  VII,  Fig.  I  shows  one  set  of  experi- 
ments of  this  kind. 

A  barrel  full  of  characteristically  spotted  apples  was  received 
in  November  from  Richland  county  and  on  the  22d,  520  of  these 
were  placed  in  the  orchard  upon  the  University  grounds.  Some  of 
the  infected  fruits  were  strung  upon  threads  and  hung  upon  the 
trees,  others  were  placed  directly  upon  the  ground,  and  others  were 
put  into  trays  made  of  wooden  frames  with  wire  screen  bottoms. 
These  were  then  securely  supported  at  varying  distances  from  the 
ground  to  test  what  effect  this  distance  might  have.  None  of  these 
apples  produced  spores  or  showed  other  evidence  of  the  vitality  of 
the  fungus  in  the  spring.  All  were  softened  by  water  and  various 
rot-producing  agents.  This  was  true,  let  it  be  understood,  of  those 
hung  upon  the  trees  as  well  as  those  on  or  near  the  ground.  The 
explanation  is  that  these  apples  were  not  dried  out  when  so  hung 
up,  and  at  that  season  of  the  year  with  the  conditions  which  pre- 
vailed they  did  not  become  dry  enough  to  be  preserved  from  other 
rots. 

The  evidence  seems  abundant  and  conclusive.  It  cannot  be  said 
that  the  fungus  never  lives  over  winter  in  old  infected  fruit  lying 
on  the  ground,  but  if  it  does  occur  in  nature,  it  must  be  in  very 
rare  cases.  The  only  exception  which  has  been  witnessed  was  in 


1907.}        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  585 

regard  to  a  few  hardened  specimens  which  were  placed  while  they 
were  dry  in  a  muslin  sack  after  the  ground  was  frozen  and  laid  un- 
der the  shelter  of  a  Norway  spruce  hedge.  This  is  really  no  excep- 
tion to  the  statement  as  applied  to  the  apples  as  they  naturally  fall 
from  the  trees.  It  may,  however,  occur  that  some  mummies  which 
have  hung  through  the  winter  on  the  trees  fall  or  become  knocked 
off  so  late  in  the  spring  that  the  fungus  can  survive  long  enough  to 
perpetuate  itself  in  new  infection.  This  in  a  practical  sense  appears 
to  be  the  only  danger  from  the  old  apples  found  on  the  ground.  Plate 
VIII.,  Fig.  2,  shows  a  mummified  Willow  apple  which  was  picked 
up  with  many  others  under  a  tree  in  Clay  county,  Illinois,  on  June 
24,  1907.  The  fruit  on  this  tree  was  practically  all  destroyed  by 
bitter  rot  occurring  late  the  preceding  season.  The  apple  shown 
was  still  firm  in  texture  and  upon  incubating  produced  spores  which 
in  the  photograph  print  show  as  small  white  dots  or  spots.  No 
others  among  the  250  specimens  picked  up  with  this  gave  any  evi- 
dence, under  similar  treatment,  of  spore  production,  while  9  out  of 
1 8  taken  from  the  tree  where  they  had  hung  over  winter  gave  forth 
spores  just  as  did  this  particular  specimen.  An  examination  of  the 
stem  of  this  apple  revealed  clearly  enough  that  it  had  only  recently 
fallen,  for  the  marks  of  recent  separation  were  plainly  seen.  The 
photographic  reproduction,  (PI.  IV.,  Fig.  3,)  shows  this,  but  not  so 
satisfactorily  as  did  the  specimen  itself. 

May  separate  spores  survive  in  or  on  the  earth  so  as  to  carry 
the  infective  agent  over  from  season  to  season? 

From  laboratory  experience  it  cannot  be  considered  possible  that 
spores  of  the  bitter  rot  fungus  washed  from  infected  fruits  to  the 
ground  may  long  retain  their  vitality.  If  the  temperature  permits, 
they  quickly  germinate  and  in  this  way  exhaust  themselves  and  then 
die  from  want  of  nourishment.  Deprived  of  the  protecting  coating, 
they  soon  die  by  drying,  if  they  are  not  favored  by  conditions  con- 
ducive to  germination. 

But  to  leave  nothing  undone  attempts  were  made  to  determine 
the  facts  by  experimental  methods.  Direct  search  was  first  made  by 
microscopic  examinations  in  June  for  the  spores  in  the  dirt  and 
among  the  trash  under  trees  upon  which  there  had  been  the  year 
before  a  great  amount  of  bitter  rot.  It  was  ascertained  that  the 
spores  of  this  fungus  can  be  found  again  after  they  have  been  re- 
cently mixed  with  such  dirt  by  treating  the  earth  with  a  small 
quantity  of  water,  stirring  well,  allowing  slight  settlement,  and  ex- 
amining under  the  microscope  the  material  remaining  on  or  near  the 
surface  of  the  water.  After  considerable  practice  with  earth  in 


580  BULLETIN  No.  118.  [September, 

which  spores  had  been  purposely  placed  just  previously,  and  by 
methods  determined  by  such  practice,  careful  and  extended  search 
was  made  of  the  earth  and  trash  under  previously  infected  trees. 
Many  spores  of  various  kinds  were  seen,  but  in  no  case  were  there 
any  Glceosporium.  It  was  confidently  believed  they  could  be  found, 
at  least  occasionally,  if  they  were  present  in  any  considerable  num- 
ber, in  the  materials  examined.  A  long  search  gave  only  negative 
results. 

Trial  was  made  by  inoculations  in  fruit  half  or  more  grown. 
Earth  in  which  a  few  fresh  spores  were  mixed  was  placed  under 
the  skin  of  the  apples  by  means  of  a  scalpel  and  in  a  few  days  after 
proper  incubation  the  characteristic  spots  of  the  rot  appeared.  Nu- 
merous similar  inoculations  into  the  same  kind  of  apples  of  earth 
from  under  trees  badly  infected  the  year  before  were  never  fol- 
lowed by  a  similar  result,  though  the  tests  were  very  numerous. 

Still  another  method,  believed  to  be  more  conclusive,  was  thor- 
oughly tried — to  the  extent  of  several  hundred  tests.  The  best  ap- 
ples for  the  purpose  which  could  be  obtained  in  June  and  July  were 
used  in  these  experiments.  They  were  Maiden  Blush  in  the  market 
from  the  South ;  a  very  early  variety,  nearly  ripe,  locally  known  as 
Britton's  Early,  and  Chenango  (Sherwood's  Favorite),  also  quite 
mature,  both  taken  from  the  trees.  Tin  pans  about  8  inches  in  di- 
ameter and  3  inches  deep  were  used  in  pairs,  one  as  a  dish  and  one 
as  a  cover,  to  form  a  culture  box.  The  test  apples,  some  of  which 
were  punctured  in  many  places  with  a  needle  to  favor  infection, 
were  buried  in  moistened  earth  placed  in  these  pans,  sometimes 
mixed  with  fresh  bitter  rot  spores,  in  other  cases  from  under  trees 
on  which  the  fruit  had  badly  rotted  the  year  before.  Temperature 
conditions  were  made  favorable  for  the  development  of  bitter  rot. 

The  results  showed  characteristic  infection  in  about  75  percent 
of  the  tests,  in  which  the  spores  were  added  to  the  soil,  but  in  no  case 
not  under  suspicion  when  earth  without  such  spore  addition  was 
used.  In  fact,  however,  there  were  two  positive  results  when  no 
spores  were  placed  in  the  earth,  one  upon  a  Maiden  Blush  and  one 
on  a  Chenango  apple ;  but  the  latter  was  taken  from  a  tree  on  which 
there  were  at  the  time  apples  spotted  with  the  disease,  and  the  other 
had  been  in  the  same  paper  sack  with  it.  Since  these  proved  to  be 
so  exceptional  among  the  large  number  it  is  reasonable  to  infer  that 
these  two  apples  were  infected  or  had  spores  on  them  when  they 
were  put  into  the  'dirt.  It  was  a  fault  in  the  experiment  that  it  was 
permitted  to  be  open  to  'this  suspicion,  but  could  not  be  remedied 
after  the  test  was  made,  and  the  facts  demand  reporting. 


1907.]         BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  587 

Having  found,  as  it  was  believed,  that  earth  under  trees  having 
an  abundance  of  diseased  apples,  the  previous  year,  carried  no  in- 
fection, an  attempt  was  made  to  determine  by  the  same  method  how 
long  such  infection  continues  after  fresh  spores  are  added  to  the 
earth.  As  has  been  stated,  positive  results  very  commonly  followed 
when  fresh  spores  were  added  to  the  earth  just  as  the  test  was  to  be 
made.  What  would  result  should  apples  be  placed  in  this  moistened 
earth  at  different  intervals  of  time  after  the  spores  were  added? 
Would  there  soon  come  a  change  in  the  infectiveness  of  the  earth 
due  to  the  death  of  the  spores  which  had  been  mixed  with  it?  If 
so,  when? 

Many  experiments  were  tried.  After  one  set  of  apples  had  been 
buried  two  or  three  clays,  under  conditions  all  the  time  favorable  to 
the  germination  of  the  spores,  they  were  removed  and  another  set 
of  apples  were  placed  in  the  same  dirt;  then  after  a  similar  period 
others  were  tried.  If  such  tests  should  be  made  again,  the  pro- 
cedure would  be  somewhat  modified,  but  the  results  (see  data  fol- 
lowing, Expts.  26-29)  satisfactorily  show  that  in  the  soil  so  situated 
the  vitality  of  these  spores  is  of  short  duration, — it  is  a  question  at 
most  of  four  or  five  days.  In  none  of  the  tests  was  ihere  evidence 
that  it  is  more  tfian  four  days.  While  the  rot  spots  were  numerous 
on  the  apples  of  the  first  set  left  in  the  inoculated  soil  three  days, 
they  werexfew  on  the  set  which  immediately  followed,  i.  e.  upon 
those  put  into  the  soil  three  days  (72  hours)  after  the  spores  had 
been  stirred  into  the  earth,  and  then  none  on  the  apples  of  subse- 
quent sets. 

The  only  explanation  of  these  results  is  that  the  spores  die, 
through  germination  or  otherwise,  when  placed  in  moist  soil  in  the 
summer  time  within  a  period  not  much  more  than  seventy-two 
hours.  This  entirely  corresponds  with  what  is  known  otherwise 
concerning  the  behavior  of  Glceosporium  spores.  If  they  are  kept 
dry  in  the  condition  otherwise  than  they  are  in  when  exuding 
from  the  pustules,  they  do  live  for  months;  but  this  can  never  be 
the  case  while  they  are  in  the  ordinary  soil  of  orchards  in  our  part 
of  the  country.  We  may  confidently  conclude  there  is  nothing  in 
such  soil  over  winter  and  through  the  spring  season  which  can 
give  origin  to  an  outbreak  of  the  disease  the  succeeding  summer. 

Does  the  fungus  in  any  stage  or  in  any  manner  live  from  sea- 
son to  season  on  anything  else  besides  the  apple  tree  and  its  fruit? 
It  is  well  known  that  it  does  grow  as  a  parasite  on  other  plants  or 
their  products,  and  it  does  lead  very  readily  a  saprophytic  existence, 
as  is  sufficiently  shown  by  experiments.  There  are  scarcely  no 


588 


BULLETIN  No.  118.  \September, 


fruits  on  which  it  may  not  be  artificially  grown.  It  has  been  found 
spontaneously  growing  on  the  stems  of  sweet  speas.  There  is  noth- 
ing, therefore,  to  suggest  the  impossibility  of  a  first  seasonal  infec- 
tion of  apples  by  the  fungus  grown  on  something  else. 

Careful  and  long  continued  search  has  been  made  in  and  about 
the  orchards  of  the  area  of  the  State  subject  to  the  disease  without 
finding  the  least  evidence  that  the  fungus  does  develop  in  this  region 
on  anything  but  apples  and  apple-tree  limbs,  so  as  to  start  or  to  per- 
petuate orchard  infections.  Neither  does  there  seem  to  be  anything 
unexplainable  on  the  supposition  that  the  disease  on  apples  always 
comes  from  preceding  apple  or  apple-limb  infections.  The  first  apple- 
infections  in  any  season  comes  from  spores  produced  that  season 
and  only  shortly  before  from  mycelium  that  has  survived  the  win- 
ter in  the  cankered  spots  on  the  limbs  or  in  bitter-rot  mummies  and 
exclusively  or  nearly  so  from  those  that  have  dried  while  hanging 
to  the  tree  and  have  there  passed  the  winter. 

If  it  is  borne  in  mind  that  "a  little  leaven  leaveneth  the  whole 
lump"  in  this  case  quite  as  well  as  that  first  so  described,  and  if  it 
is  remembered  too  that  the  spores  can  be  carried  at  certain  times 
and  under  certain  conditions  to  a  considerable  distance  by  the  wind, 
nothing  further  is  necessary  to  account  for  the  beginning  of  rot 
wherever  it  has  been  and  probably  wherever  it  may  be  observed. 
This  ought  both  to  simplify  matters  and  to  give  renewed  encour- 
agement in  the  warfare  which  should  be  waged  in  the  manner  here- 
in suggested.  If,  during  the  winter,  the  sources  of  infection — 
cankers  and  mummies — are  absolutely  removed  from  the  trees  and 
exclusive  attention  given  to  these,  the  battle. will  be  won.  If  in  re- 
gard to  the  cankers — for  there  is  no  similar  "if"  in  regard  to  the 
mummies — the  work  in  perfection  is  sometimes  impossible,  much 
can  be  done  towards  preventing  their  formation  by  keeping  the 
twigs  and  limbs  free  from  bruises  and  by  preventing  the  disease  on 
the  fruit  by  careful  hand-picking  and  especially  at  first  by  the  thor- 
ough application  of  Bordeaux  mixture  at  the  proper  time.  That  is, 
cankers  need  not  be  allowed  to  form — at  all  events  they  need  not 
be  aided  in  formation  by  ignorant  or  careless  management — and  if 
formed,  most  of  them  can  be  seen  by  close  looking  and  can  be  re- 
moved. 

FIELD  AND  LABORATORY  DATA 

Experiment  I.  On  June  15,  1905,  some  dirt  and  trash  was  collected  in  Olney 
orchard  No.  3,  under  trees  known  to  have  been  badly  infected  with  bitter  rot  the 
previous  summer,  and  taken  to  the  laboratory  at  Olney  for  examination. 

About  a  tablespoonful  of  earth  with  some  trashy  vegetable  matter  was 
shaken  up  with  a  half-pint  of  water,  and  after  two  minutes  settling,  the  liquid 


1907.]         BITTER  EOT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  589 

was  carefully  poured  off.  After  two  minutes  more  no  spores  were  found  in  the 
surface  layer,  but  below,  1A  inch  from  the  surface,  there  were  several  spores  of 
at  least  four  kinds  suspended  in  the  water.  Among  these  were  Fusarium,  Mac- 
rosporium,  numerous  spindle-shaped,  rather  small,  probably,  uniseptate  forms, 
and  still  more  numerous  smaller,  short,  cylindrical  ones,  with  several  small  oval 
ones.  All  were  white  except  the  second  and  the  last,  which  were  slightly  tinted. 
After  pouring  from  one  vessel  to  another  five  times,  allowing  each  time 
about  a  half-minute  for  the  heaviest  material  to  settle,  and  decanting,  the  liquid 
was  placed  in  a  ipo  c.  c.  graduate  and  allowed  to  settle  36  hours.  The  follow- 
ing day  the  precipitate  was  examined  and  but  few  spores  of  any  kind,  were 
found.  Some  dark  colored  kinds  had  not  germinated,  but  most  of  the  hyaline 
ones  had  thrown  out  long,  slender  germ  tubes.  No  bitter  rot  spores  were  found. 
After  many  trials  it  was  learned  that  most  spores  of  various  kinds  were  to 
be  found  by  treating  the  dirt  and  trash  with  a  small  amount  of  water,  just 
enough  to  saturate  the  solid  material  and  leave  a  little  free  water,  then  after 
allowing  to  settle  about  one  minute,  to  take  a  drop  from  the  surface  for  exam- 
ination. 

On  dissolving  some  spores  of  Gleosporium  from  a  Chenango  apple  and  al- 
lowing to  stand  two  minutes  in  a  bottle  in  which  the  fluid  was  two  inches  deep, 
most  of  the  spores  were  found  near  the  surface. 

Samples  of  dirt  from  orchards  located  at  Flora,  Clay  City,  Carbondale,  and 
Ashley,  and  known  to  have  had  much  bitter  rot  the  previous  summer,  were 
treated  as  above,  and  although  various  kinds  of  spores  were  found  in  every  case, 
no  Gloeosporium  spores  were  seen. 

Experiment  2  (a).  On  June  15,  1905,  two  Maiden  Blush  apples  were  inoc- 
ulated by  inserting  dirt  into  punctures.  The  dirt  was  collected  in  Olney  orchard 
No.  2  under  a  tree  that  had  been  badly  infected  with  bitter  rot  the  past  two 
years,  (b)  Two  Maiden  Blush  apples  were  inoculated  as  above  with  similar 
dirt  collected  in  Olney  orchard  No.  3.  (c)  Some  soil  collected  under  a  maple 
tree  in  the  Olney  school-yard  was  sprayed,  until  moist,  with  water  containing 
fresh  bitter  rot  spores.  This  dirt  was  used  to  inoculate,  as  in  (a)  and  (b) 
two  Maiden  Blush  apples. 

All  the  inoculated  apples  were  placed  in  a  moist  chamber  and  occasionally 
sprayed  with  water  to  keep  them  moist.  After  four  days,  an  examination  re- 
vealed that  all  inoculations  in  (c)  showed  a  marked  development  of  bitter  rot, 
and  on  the  sixth  day  the  characteristic  pink  spores  were  oozing  through  the 
epidermis.  After  eleven  days  one  spot  of  bitter  rot  appeared  on  one  apple  of 
(a)  and  one  on  one  apple  of  (b). 

Experiment  3.  On  June  16,  four  sound  apples,  and  two  with  epidermis 
punctured  in  many  places  with  a  fine  needle,  were  covered  in  a  tin-pan  with 
moistened  dirt  and  trash  collected  in  Olney  orchard  No.  3  under  a  Ben  Davis 
tree.  The  pan  was  covered  and  kept  at  room  temperature.  After  three  days 
the  apples  were  removed  from  the  dirt  and  placed  in  a  moist  chamber.  No  bitter 
rot  developed. 

Experiment  4.  June  17.  Two  punctured  and  two  unpunctured  apples  were 
covered  in  a  pan  with  some  of  the  same  dirt  as  used  in  experiment  16,  moistened 
with  water  containing  bitter  rot  spores.  The  pan  was  covered.  After  two  days 
the  apples  were  removed  from  the  dirt  and  put  in  a  moist  chamber.  Seven  days 
later  both  punctured  apples  showed  a  number  of  bitter  rot  spots.  The  sound 
apples  were  not  infected. 

Experiment  5.  June  17.  Two  Britton's  Early  and  two  Maiden  Blush  apples, 
one  of  each  punctured,  were  covered  in  a  tin  pan  with  dirt  moistened  with 
water  containing  fresh  bitter  rot  spores.  June  19,  the  apples  were  removed  from 
the  dirt  and  kept  in  a  moist  chamber.  June  26  one  unpunctured  Maiden  Blush 
had  developed  bitter  rot  and  one  punctured  apple  had  a  soft  rot. 

Experiment  6.  June  28.  Four  Chenango  apples,  two  punctured  and  two 
sound,  were  placed  in  a  tin  pan  and  covered  with  moistened  dirt  and  litter 
collected  in  Olney  orchard  No.  2,  under  an  apple  tree  known  to  have 
had  bitter  rot  the  previous  year.  The  pan  was  covered  and  placed 
in  an  extemporized  incubator  which  registered  about  36  C.  during 
the  day.  gradually  falling  during  the  night  to  24  C.  by  7  a.m.  Aft^r  two  days 
the  apples  were  removed  from  the  dirt  and  placed  in  a  moist  chamber  at  room 


590  BULLETIN  No.  118.  [September, 

temperature.  July  7  the  two  punctured  apples  had  bitter  rot  and  one  unpunctured 
one  showed  infection  of  some  kind.  July  n  these  apples  had  bitter  rot.  It  was 
found  later  that  the  apples  used  in  the  experiment  had  been  taken  from  a  Che- 
nango  tree  that  was  much  infected  with  the  bitter  rot.  The  apples  were  sound 
when  used  in  the  experiment,  as  were  those  which  remained  in  the  sack  from 
which  they  were  taken.  Later,  however,  several  apples  in  the  bag  developed 
bitter  rot  and  it  is  probable  that  the  apples  which  developed  the  rot  after  treat- 
ment with  the  soil  were  already  infected  with  the  spores  of  bitter  rot  fungus. 
The  Maiden  Blush  apples  used  in  experiment  I  were  taken  from  the  same  bag 
as  the  Chenango. 

Experiment  7.  June  29.  Four  Britten's  Early  apples,  two  of  them  punc- 
tured, were  covered  in  a  tin  pan  with  moistened  dirt  and  trash  collected  in 
Olney  orchard  No.  4,  under  a  Ben  Davis  tree.  After  incubating  twenty-four 
hours  the  apples  were  removed  from  the  dirt  and  placed  in  a  moist  chamber  at 
room  temperature.  No  bitter  rot  developed. 

Experiment  8.  June  29.  Four  Britton's  Early  apples,  two  punctured,  were 
treated  as  those  in  experiment  6  with  moistened  dirt  and  trash  collected  in 
Olney  orchard  No.  3,  under  a  Ben  Davis  tree  known  to  have  bitter  rot  the 
previous  year.  On  July  21  no  bitter  rot  had  developed. 

Experiment  9.  June  29.  Treated  four  Britton's  Early  apples,  two  punc- 
tured, as  those  in  experiment  7  with  dirt  and  trash  collected  in  the  Olney  or- 
chard No.  3,  under  a  Ben  Davis  tree  known  to  have  had  the  rot  the  previous 
year,  and  which  developed  it  later  the  same  season.  No  bitter  rot  developed. 

Experiment  10.  June  29.  A  duplicate  of  experiment  8.  No  bitter  rot 
developed. 

Experiment  II.  June  29.  Four  apples  were  treated  as  those  in  experiment 
7  with  dirt  and  trash  collected  in  Olney  orchard  No.  3,  under  a  Ben  Davis  tree 
which  had  bitter  rot  the  previous  year  and  which  developed  it  later  the  same 
season.  No  development  of  bitter  rot  took  place. 

Experiment  12.  June  29.  Four  Red  Astrachan  apples  were  treated  as  those 
above  with  moistened  dirt  and  litter  collected  in  an  orchard  at  Ashley,  111.  No 
bitter  rot  developed. 

Experiment  13.  (a)  June  29.  Four  Red  Astrachan  apples  were  treated  as 
above  with  moistened  dirt  from  the  Olney  school-yard.  July  21  one  apple  had 
decayed  with  a  soft  rot.  No  bitter  rot  developed,  (b)  June  29.  Four  "Briton's 
Early"  apples  were  treated  as  above  with  some  of  the  same  kind  of  dirt  used 
in  (a).  No  bitter  rot  developed,  (c)  June  29.  Four  Red  Astrachan  apples  were 
treated  as  those  in  (a)  and  (b)  with  some  of  the  same  kind  of  dirt  moistened 
with  water  containing  bitter  rot  spores.  July  7  one  punctured  apple  had  fifteen 
spots  of  bitter  rot,  the  other  one  ten.  July  17  all  four  apples  had  developed 
bitter  rot. 

Experiment  14.  July  7.  Four  Red  Astrachan  apples,  two  punctured  and 
two  sound,  were  placed  in  a  tin  pan  and  covered  with  moistened  dirt  and  trash 
collected  in  an  orchard  at  Clay  City,  111.,  in  an  orchard  which  suffered  very 
much  from  bitter  rot  the  previous  year.  After  incubating  sixty  hours  the  apples 
were  removed  and  kept  in  a  moist  chamber  at  room  temperature.  After 
fourteen  days  three  apples  were  infected  with  black  rot.  No  bitter  rot  developed. 

Experiment  15.  July  7.  Four  apples,  two  Britton's  Early  and  two  Early 
Harvest,  one  of  each  punctured,  were  treated  as  those  in  experiment  13.  No 
bitter  rot  developed. 

Experiment  16.  July  7.  Four  Red  Astrachan  apples,  two  punctured,  were 
treated  as  those  above  with  dirt  and  trash  collected  in  an  orchard  at  Carbon- 
dale,  111.,  and  said  to  have  been  badly  infected  with  bitter  rot  the  previous  year. 
No  bitter  rot  development  took  place. 

Experiment  17.  July  7.  Four  apples,  two  Early  Transparent  and  two  Early 
Harvest,  one  of  each  punctured,  were  treated  as  those  in  experiment  15.  Bitter 
rot  failed  to  develop. 

Experiment  18.  July  7.  Two  Early  Harvest  and  two  Red  Astrachan  apples, 
one  of  each  punctured,  were  treated  as  those  in  experiment  16,  with  dirt  from 
the  same  orchard,  but  collected  under  a  different  tree.  After  fourteen  days  no 
bitter  rot  developed. 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  591 

Experiment  19.  July  7.  Two  Early  Harvest  and  two  Early  Transparent 
apples,  one  of  each  punctured,  were  treated  with  dirt  collected  under  a  third 
tree  in  the  last  mentioned  orchard.  Juy  21  no  bitter  rot  had  developed. 

Experiment  20.  July  7.  This  experiment  was  made  as  a  check  to  the  six 
preceding  experiments.  Four  Briton's  Early  apples,  two  punctured,  were  treated 
as  above  with  dirt  from  the  Olney  school-yard  moistened  with  water  containing 
bitter  rot  spores.  July  II  one  unpunctured  apple  had  a  soft  rot.  No  bitter  rot 
developed. 

Experiment  21.  This  experiment  was  made  in  order  to  determine  whether, 
while  exposed  in  the  laboratory  for  several  days,  the  dirt  and  trash  used  in 
experiments  I  and  5  had  become  infected  with  spores  of  bitter  rot  fungus,  (a) 
July  10  four  Britton's  Early  apples,  two  punctured,  were  placed  in  a  tin  pan, 
covered  with  some  of  the  moistened  dirt  and  trash  mentioned  above,  and  incu- 
bated 48  hours.  August  5  no  bitter  rot  had  developed.  (b)A  duplicate  of  (a). 
No  development  of  bitter  rot  was  apparent. 

From  these  results  one  would  judge  that  the  infection  of  bitter  rot  in  ex- 
periments I  and  5  was  due  not  to  spores  in  the  dirt  and  trash  used  but  to  those 
that  were  present  on  the  apples. 

Experiment  22.  July  10.  Four  Britton's  Early  apples,  two  punctured,  were 
covered  with  moistened  dirt  and  trash  collected  in  Olney  orchard  No.  3  under 
Ben  Davis  tree  X,  which  is  known  to  have  had  bitter  rot  the  two  preceding 
years  and  which  developed  it  later  the  same  season,  and  incubated  twenty-four 
hours.  At  the  end  of  this  time  they  were  placed  in  a  moist  chamber  at  room 
temperature.  There  was  no  development  of  bitter  rot. 

Experiment  23.  July  10.  A  duplicate  of  experiment  22  except  that  the 
apples  were  treated  with  dirt  from  Ben  Davis  tree  next  north  of  X.  Bitter  rot 
failed  to  develop. 

Experiment  24.  On  July  10  four  Britton's  Early  apples,  two  punctured,  were 
treated  as  above  with  dirt  and  trash  collected  under  a  Ben  Davis  tree  not  far 
from  the  one  mentioned  in  experiment  23,  and  known  to  have  had  bitter  rot  the 
preceding  year.  No  bitter  rot  developed. 

Experiment  25.  July  10.  Four  Maiden  Blush  apples,  two  punctured,  were 
treated  as  those  in  experiment  24  with  dirt  and  litter  collected  in  Clay  City  or- 
chard No.  i,  an  orchard  badly  infected  the  previous  two  or  three  years  with 
bitter  rot.  There  was  no  development  of  bitter  rot. 

Experiment  26.  This  and  the  two  following  experiments  were  made  for  the 
purpose  of  determining  how  long,  after  inoculation  with  spores,  dirt  would  be 
capable  of  producing  an  infection  of  bitter  rot  on  apples  buried  in  it  and  sub- 
jected to  different  temperatures.  The  dirt  used  in  these  experiments  was  some 
of  the  same  kind  of  dirt  used  in  check  experiments  already  given,  being  free 
from  bitter  rot  spores.  July  II.  (a)  Four  Britton's  Early  apples  two  punc- 
tured, were  covered  with  dirt  moistened  with  a  suspension  of  spores  in  water,  and 
incubated  forty-eight  hours.  At  the  end  of  this  time  the  apples  were  removed 
and  kept  in  a  moist  chamber  at  room  temperature.  On  July  21  two  apples  had 
bitter  rot  and  a  third  developed  it  a  day  later,  (b)  Two  Britton's  Early  apples, 
one  punctured,  were  put  into  the  same  dirt  used  in  (a)  on  July  13,  and  incubated 
four  days.  Both  apples  rotted  with  a  soft  rot,  aided  quite  probably  by  a  too  long 
period  of  incubation,  (c)  On  July  21  four  days  after  the  removal  of  the  apples  in 
(b)  from  the  dirt,  two  Britton's  Early  apples,  one  punctured,  were  placed  in  the 
same,  remoistened,  and  incubated  three  days.  July  24  the  apples  were  removed 
from  the  dirt  and  both  were  found  to  be  infected  with  what  afterwards  proved 
to  be  a  soft  rot.  No  bitter  rot  developed,  (d)  As  a  check  four  Maiden  Blush 
apples  were  treated  with  the  same  kind  of  soil,  but  without  the  spores.  No 
bitter  rot  developed. 

Experiment  27.  In  this  experiment,  begun  July  u,  the  apples  were  always 
kept  at  room  temperature,  otherwise  they  were  treated  about  as  the  above.  But 
two  apples  were  used  in  (a),  (a)  July  21  the  punctured  apples  had  developed 
bitter  rot  and  by  July  29  the  other  showed  infection,  (b)  The  apples  were  put 
into  the  dirt  July  13  and  were  removed  July  15.  Six  days  later  one  apple  had 
developed  bitter  rot,  and  the  other  a  soft  rot.  (c)  Two  apples,  one  punctured, 
were  placed  in  the  same  dirt  used  in  (b)  on  July  21,  and  removed  July  24  when 
they  were  placed  under  moist  conditions.  No  bitter  rot  developed. 


592 


BULLETIN  No.  118 


[September, 


Experiment  28.  This  experiment  is  practically  a  repetition  of  experiment 
27  but  with  this  difference  that  the  apples  were  kept  in  a  moist  condition  under 
a  tree  in  the  open,  (a)  On  July  n  two  Britton's  Early  apples,  one  punctured, 
were  covered  with  the  moistened  dirt  containing  the  spores  of  bitter  rot.  July 
13  the  apples  were  removed  from  the  dirt.  Eight  days  later  both  apples  showed 
development  of  bitter  rot.  (b)  July  13  two  apples,  one  punctured,  were  placed 
in  the  dirt  of  (a)  and  left  for  four  days.  July  21  both  apples  had  developed  a 
soft  rot  but  no  bitter  rot.  (c)  Two  sound  apples,  one  punctured,  were  placed  in 
the  dirt  used  in  (b)  on  July  21.  After  three  days  they  were  removed  and  kept 
moist.  No  bitter  rot  developed. 

Experiment  29.  This  series  of  tests,  quite  similar  to  experiments  26,  27, 
and  28,  was  made  further  to  test  the  point  in  question  in  the  preceding  experi- 
ments. The  soil  was  of  the  same  kind  as  that  used  in  the  three  preceding  ex- 
periments and  was  moistened  with  water  containing  bitter  rot  spores. 

There  were  two  sets  of  five  pans  each,  carried  on  at  the  same  time.  Each 
pan  contained  two  apples,  one  of  them  punctured.  Set  one  was  incubated,  while 
set  two  was  always  kept  at  room  temperature.  After  three  _to  four  days  the 
apples  were  removed  from  the  pans  and  kept  in  moist  chambers  at  room  tem- 
perature, and  fresh  apples  were  put  in  the  same  dirt  to  be  subsequently  treated 
in  same  way.  Shown  in  tabulated  form  the  results  were  as  follows : 


c 
£ 

Started. 

Removed 
from  dirt. 

Apples 
infected.! 

Started. 

Removed  1 
from  dirt. 

Apples 
infected 

Started. 

Removed 
from  dirt. 

Apples 
infected. 

Started. 

Removed 
from  dirt. 

Apples 
infected. 

1 

July 
14 

July 
17 

1 

July 
17 

July 
21 

O 

July 
21 

July 
24 

O 

July 

27 

July 
31 

0 

2 

" 

" 

1 

« 

« 

O 

« 

» 

0 

•• 

" 

O 

a 

3 

» 

" 

1 

« 

« 

O 

« 

» 

0 

" 

" 

O 

4 

» 

« 

1 

« 

" 

0 

« 

" 

0 

« 

» 

O 

5 

" 

u 

0 

" 

» 

O 

" 

« 

o 

« 

» 

O 

1 

» 

" 

0 

« 

- 

1 

" 

" 

0 

» 

" 

O 

2 

« 

" 

1 

« 

" 

0 

" 

" 

o 

« 

« 

0 

(M 

u 

3 

M 

« 

2 

•' 

» 

O 

» 

•« 

0 

» 

» 

O 

4 

" 

« 

2 

« 

» 

1 

« 

" 

o 

" 

« 

o 

5 

" 

" 

2 

» 

" 

0 

" 

« 

0 

•' 

» 

o 

The  pans  with  the  apples  in  dirt  of  the  first  set  were  placed  in  the  incubator 
— 3O  to  36  degrees  C. — and  remained  there  24  hours,  after  which  they  were  kept 
at  room  temperature  two  more  days.  Those  of  the  second  set  were  kept  from 
the  beginning  at  the  temperature  of  the  room.  It  will  be  seen  that  of  the  40 
apples  tried  13  became  infected,  all  but  two  of  which  were  among  those  first 


1907.]         BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  593 

put  into  the  dirt  and  these  two  were  among  those  that  next  followed.  The 
spores  evidently  lived  longer  in  the  set  kept  at  room  temperature  where  we 
know  they  would  be  somewhat  slower  in  germinating. 

Experiment  30.  The  purpose  of  these  tests  was  to  determine  whether  the 
spores  of  the  bitter  rot  fungus  in  the  dirt  and  trash  under  infected  trees,  if 
any  are  present,  can  be  washed  out  with  water  and  used  in  suspension  to  infect 
apples.  Including  the  check  ten  tests  were  made.  The  dirt  and  trash  used  in 
the  nine  tests  was  collected  under  trees  known  to  have  had  the  bitter  rot,  and 
some  of  which  had  been  tested  in  former  experiments,  (a)  Check.  July  II 
some  dirt  from  the  school-yard  was  sprayed  with  spores  in  solution,  thoroughly 
stirred  and  mixed,  and  allowed  to  settle.  After  adding  water  until  it  stood  an 
inch  or  inore  above  the  dirt,  it  was  again  stirred  and  mixed  urttil  every  portion 
of  the  dirt  and  trash  had  been  washed.  After  settling  the  water  was  poured  off 
and  in  it  were  placed  two  apples,  one  punctured,  and  the  whole  incubated  for 
twenty-four  hours.  At  the  end  of  this  time,  July  12,  the  apples  were  removed 
from  the  incubator  and  two  days  later  from  the  water.  They  were  kept  in  a 
moist  chamber  at  room  temperature.  Bitter  rot  developed  on  the  punctured 
apple,  (b)  July  n  dirt  and  trash  collected  in  Olney  orchard  No.  3  under  Ben 
Davis  tree  XI  was  treated  as  that  in  (a)  with  the  exception  that  no  spores  of 
bitter  rot  were  added.  After  thirteen  days  one  apple  developed  a  spot  of  bit- 
ter rot. 

There  was  no  bitter  rot  development  in  any  of  the  remaining  eight  tests. 
Experiment  31.  July  17.  The  dirt  and  trash  used  in  this  experiment  was 
collected  July  15,  tinder  an  apple  infected  with  bitter  rot  hanging  on  a  Ben  Davis 
tree  in  Olney  orchard  No.  3.  (a)  As  in  previous  tests,  the  dirt  was  moistened 
and  into  it  were  placed  four  sound  apples,  two  punctured.  They  were  incubated 
for  twenty- four  hours  and  on  July  21  removed  from  the  dirt  and  placed  in  a 
moist  condition  at  room  temperature.  One  apple  developed  bitter  rot. 

Two  other  tests  (b)  and  (c)  were  made  as  (a)  with  no  development  of 
bitter  rot. 

Experiment  32.  The  dirt  used  in  this  experiment  was  collected  in  two  or- 
chards at  Kell,  111.,  July  18.  (a)  Dirt  collected  in  Kell  orchard  No.  i  under  a 
Lowell  tree  bearing  many  infected  apples.  After  moistening  the  soil  four 
Britton's  Early  apples  were  covered  with  it  and  incubated  thirty  hours.  No  bitter 
rot  ever  developed,  (b)  This  test  was  carried  on  as  (a)  but  with  the  difference 
that  dirt  and  trash  from  under  another  tree  was  used.  Bitter  rot  failed  to  de- 
velop, (c)  The  dirt  and  trash  used  in  this  test  was  collected  under  a  Northern 
Spy  tree  in  Kell  orchard  No.  2.  No  development  of  bitter  rot.  : 

Experiment  33.  Since  one  apple  in  (b)  experiment  30  developed  bitter  rot, 
two  additional  tests  of  some  of  the  same  soil  were  made,  (a)  To  the  water 
extract  of  the  dirt  and  trash  two  apples,  one  punctured,  were  added  and  incu- 
bated twenty-four  hours.  One  spot  of  bitter  rot  developed,  (b)  Duplicate  of 
(a).  No  development  of  bitter  rot. 

Experiment  34.  July  25.  This  experiment  consisted  of  three  tests,  two  with 
dirt  from  the  school-yard  and  which  had  been  exposed  sometime  in  the  labora- 
tory and  one  with  fresh  dirt  from  the  same  source,  to  which  was  added  spores 
of  bitter  rot  fungus  in  water,  (a)  To  some  of  the  former  dirt,  four  apples 
two  punctured,  were  added  and  incubated  twenty-four  hours.  After  a  number 
of  days  no  bitter  rot  had  developed,  (b)  Duplicate  of  (a).  No  bitter  rot  ap- 
peared, (c)  The  treated  fresh  dirt  from  the  school-yard  to  which  four  apples, 
two  punctured,  were  added,  was  incubated  twenty-four  hours.  One  apple  de- 
veloped bitter  rot. 

Experiment  35.  Not  feeling  satisfied  with  the  results  of  experiment  31, 
this  experiment  consisting  of  two  parts  of  five  tests  each,  was  made.  Two 
checks  were  used. 

PART  I. 

(a)  In  the  water  extract  of  some  of  the  same  dirt  as  that  used  in  experi- 
ment 31  were  placed  two  Red  Astrachan  apples,  one  punctured.  After  incubating 
twenty-four  hours  the  pan  was  removed,  and  two  days  later  the  apples  were 
taken  from  the  water  and  kept  in  a  moist  chamber  at  room  temperature. 

Tests  b,  c,  d,  and  e,  were  duplicates  of  (a).  No  bitter  rot  developed  in 
any  of  the  tests. 


594  BULLETIN  No.  118.  [September, 

(f)  The  check  consisted  of  a  water  extract  of  dirt  from  the  school-yard,  to 
which  spores  of  bitter  rot  fungus  had  previously  been  added,  with  two  apples, 
one  punctured.  They  were  incubated  twenty-four  hours  and  two  days  later 
removed  from  the  water.  Both  apples  developed  bitter  rot. 

PART  II. 

These  tests  were  made  with  some  of  the  same  dirt  as  that  used  in  Part  I, 
moistened  and  covered  over  the  apples.  All  five  tests  were  made  at  the  same 
time  and  alike.  There  was  no  bitter  rot  development  in  any  case. 

(c)  The  check  was  made  with  inoculated  school-yard  dirt.  Bitter  rot  failed 
to  develop. 

Experiment  36.  This  experiment  was  made  to  determine,  if  possible,  how 
long  bitter  rot  spores  would  remain  in  a  living  condition  in  the  soil  in  the 
orchard  and  be  capable  of  producing  bitter  rot  of  apples  which  were  buried  in 
this  infected  soil.  The  experiment  was  made  in  the  orchard  of  the  Horticultural 
Department  of  the  University  of  Illinois,  and  consisted  of  a  series  of  five  tests. 
After  the  apples  had  remained  in  the  soil  three  or  four  days  they  were  replaced 
with  sound  ones  and  the  former  were  brought  to  the  laboratory  for  further  de- 
velopment, (a)  An  area  of  soil  eighteen  inches  square  was  selected  under  an 
apple  tree  and  the  first  four  inches  was  well  stirred  and  moistened  with  water 
containing  many  spores  of  the  bitter  rot  fungus.  After  burying  ten  apples,  five 
punctured,  in  the  dirt,  it  was  again  sprinkled  with  the  infected  water.  Three  days 
later  the  apples  were  removed  to  the  laboratory.  Four  apples,  three  punctured 
and  one  unpunctured,  developed  bitter  rot.  (b)  Duplicate  of  (a)  under  tree 
No.  2.  Eight  apples  developed  bitter  rot.  (c)  Duplicate  of  (a)  under  tree  No. 
3.  Seven  apples  developed  bitter  rot.  (d)  Duplicate  of  (a)  under  tree  No.  4. 
Three  apples  developed  bitter  rot.  (e)  Check.  No  spores  were  added  to  dirt 
in  this  test  made  under  tree  No.  5,  but  otherwise  treated  as  the  other  tests.  No 
development  of  bitter  rot  took  place. 

On  July  25  when  the  apples  of- the  tests  just  mentioned  were  removed  from 
the  soil  sound  ones  were  put  in.  Fourteen  days  later  these  were  removed  to 
the  laboratory.  The  soil  was  rather  dry  the  first  eight  days,  but  on  September  2 
a  heavy  shower  came  and  the  soil  was  in  excellent  condition  for  the  germination 
of  any  spores  that  might  be  there,  (a)  Under  tree  No.  I.  Five  apples  developed 
bitter  rot.  (b)  Tree  No.  2.  Two  apples  became  infected  with  bitter  rot.  (c) 
Tree  No.  3.  Two  apples  infected,  (d)  Tree  No.  4.  No  bitter  rot.  (e)  Apples 
were  not  put  in  the  soil  this  time. 

The  experiment  was  unavoidably  ended  at  this  time.  There  was,  however,  a 
considerable  decrease  in  the  number  of  bitter  rot  apples  in  the  last  test,  and 
judging  from  this  fact  and  from  former  results  obtained  in  the  laboratory,  the 
life  of  bitter  rot  spores  in  soil  is  quite  short  and  incapable  of  perpetuating  itself 
any  length^of  time. 

,  ABSOLUTE  ERADICATION 

The  entire  eradication  of  the  disease  from  an  orchard  is  cer- 
tainly possible.  Notwithstanding  the  facts  made  known  herein  and 
elsewhere  concerning  the  persistence  of  vitality  on  the  part  of  the 
fungus  and  concerning  the  dissemination  of  its  spores,  the  fuller 
studies  make  this  statement  less  hazardous  than  it  might  have  been 
previously.  We  have  seen  that  the  spores  can  be  carried  while 
capable  of  germination  by  the  wind,  and  it  cannot  be  doubted  that 
the  disease  is  sometimes  by  this  means  widely  distributed.  But  in- 
stances of  this  are  evidently  exceptional,  for  it  is  well  known  that 
the  malady  often  persists  in  a  remarkable  manner  in  some  special 
portion  of  an  orchard — in  one  comer,  along  one  side,  near  the  pack- 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  595 

ing  shed,  etc.,  while  for  a  long  time  it  does  not  appear  on  the  trees 
elsewhere  in  the  orchard,  though  these  are  of  the  same  kind  and  are 
in  every  way  as  susceptible  as  are  those  affected.  This  means  that, 
as  a  rule,  the  disease  does  not  spread  rapidly  into  new  territory. 
We  now  know  it  may  occasionally  take  long  leaps,  but  the  occasions 
are  not  commonly  frequent.  It  is  easy  enough  to  understand  that 
when  such  leaps  occur  the  living  spores  must  not  only  be  carried  to  a 
distance,  but  they  must  fall  on  fruits  and  must  there  find  conditions 
suitable  for  their  germination  and  the  penetration  of  the  epidermis. 
While  there  may  be  spores  enough  and  wind  enough,  there  may 
readily  be  failure  otherwise.  That  there  is  such  failure  is  sufficiently 
shown  by  abundant  observation. 

It  is  no  longer  doubtful  that  a  crop  of  apples  can  be  saved  by 
spraying  with  Bordeaux  mixture.  Let  it  be  remembered  that  this 
work  thoroughly  well  done  does  more  than  to  save  the  crop.  It 
helps  also  to  save  subsequent  crops.  The  disease  is  to  be  fought  to 
a  finish,  and  for  success  must  be  attacked  from  all  quarters.  Less 
development  on  the  fruit  means  less  chance  for  winter  survival.  Re- 
striction of  the  latter  means  less  liability  of  fruit  infection.  Sum- 
mer spraying  and  winter  inspection  of  the  trees  should  both  be 
prosecuted  and  should  be  energized  with  the  reasonable  hope 
founded  in  ascertained  facts  that  complete  and  permanent  victory  is 
attainable,  and  is  attainable  by  ways  and  means  now  well  under- 
stood. Other  information  of  much  value  may  hereafter  be  added, 
but  no  one  should  wait  for  it ;  neither  is  there  any  excuse  for  spend- 
ing strength  and  time  upon  methods  or  processes  which  have  not 
the  support  of  well  worked  out  and  conclusive  experimental  tests. 
It  is  idle  to  shoot  without  first  taking  true  aim;  it  is  worse  than 
useless  to  fire  with  ammunition  which  from  its  nature  makes  ef- 
ficiency impossible.  It  is  exceedingly  desirable  to  experiment  if  one 
understands  what  he  is  doing;  it  is  well-nigh  shameful  to  draw 
conclusions  from  the  supposed  results  of  irrevalent  tests.  It  never 
can  be  too  well  understood  that  not  only  are  effects  produced  by 
causes,  but  that  certain  and  definite  effects  are  due  to  certain  and 
definite  causes.  We  cannot  mix  cause  and  effect  and  get  true  ex- 
planations. "One  cannot  make  a  silk  purse  out  of  a  sow's  ear." 
One  cannot  pack  apples  in  a  barrel  by  means  of  a  sewing  machine. 
The  bitter  rot  fungus  is  the  only  thing  that  makes  the  spots  of  bit- 
ter rot  on  apples.  Hail  cannot  do  it.  Hot  weather  cannot  do  it. 
Copper  sprays  cannot  do  it.  Evil  minded  persons  cannot  do  it. 
Nor  can  neglect  and  shiftlessness  be  the  direct  agents  in  the  produc- 
tion of  these  well-recognized  and  much  dreaded  tokens  of  great  fi- 


596  BULLETIN  No.  118.  [September, 

nancial  loss.  This  agent  is  the  fungus,  and  it  is  with  this  that  we 
must  deal,  pointedly,  directly,  purposely;  and  we  must  fight  with 
weapons  suftable  to  this  particular  warfare.  If  it  were  folly  to  try 
to  catch  wolves  with  T)irdlime,  or  to  take  fish  in  pitfalls,  it  is  no  less 
so  to  try  to  head  off  bitter  rot  with  a  plow  or  with  poison  well  suited 
to  stop  the  attacks  of  codling  moths. 

The  first  thing  to  do  is  clearly  to  recognize  the  enemy,  then 
strike  when  and  where  and  how  he  may  be  reached.  In  this  case  the 
foe  is  now  well  known ;  there  is  no  longer  any  room  for  doubt  as 
to  what  the  agent  of  injury  is,  nor  as  to  the  depredator's  mode  of 
life  and  action ;  neither  should  there  be  hesitation  concerning  meth- 
ods of  combat.  Some  very  sensible  new  way  of  procedure  may  be 
discovered,  but  the  time  has  gone  by  for  any  sort  of  hit  and  miss  at- 
tempts not  founded  on  existing,  and  any  possible  further,  actual 
knowledge. 

Putting  down  in  a  few  words  what  all  this  means  it  may  be 
said :  The  fungus,  Glomerella  rufomaculans,  is  the  active  agent  in 
the  apple  injury  known  as  bitter  rot.  It  lives  over  winter  in  limb- 
cankers  and  in  mummies  that  have  not  been  much  subjected  to  other 
rots  and  this  mostly  means  those  that  have  hung  on  the  trees  from 
the  preceding  season.  Newly  formed  spores  begin  to  issue  as  early 
as  the  weather  conditions  permit,  sometimes  by  the  ist  of  June  in 
South-central  Illinois  from  cankers  and  tree-hanging  mummies,  and 
they  may  be  produced  within  one  week's  time  after  infection  on  new 
fruits.  Spores  are  distributed  by  insects  (especially  by  so-called 
pomace  flies),  by  water  as  it  drips  from  above  in  a  tree,  or  is  splashed 
from  tree  to  tree  in  storms,  and  by  wind ;  but  with  all  these  means 
distribution  is  very  irregular  and  not  usually  rapid  or  extensive 
compared  with  what  occurs  in  connection  with  many  other  plant 
diseases  due  to  fungi,  as  for  instance  apple  scab,  and  black  rot  of 
grapes.  Spores  can  germinate  and  cause  infection  of  fruit  only 
when  there  is  sufficient  moisture  on  their  surfaces ;  when  the  air  is 
continuously  dry  infection  cannot  occur;  this  always  takes  place 
when  it  does  occur  from  outside  and  in  no  other  way  than  by  germ- 
tubes  of  spores  (including  appressoria).  There  are  two  methods  of 
directly  combating  the  fungus,  viz.,  (i)  cutting  off  and  hand-pick- 
ing the  cankers  and  old  mummies;  and  (2)  spraying  with  Bor- 
deaux mixture.  The  first  is  best  done  when  the  leaves  are  off  and 
it  is  abundantly  worth  while  to  do  it  thoroughly.  If  it  were  pos- 
sible to  remove  every  limb  and  twig  infection  (which  may  not  be 
possible)  and  then  take  off  all  old  infected  fruits  (which  is  possible) 
the  disease  would  be  controlled  in  ordinary  cases.  The  spray  must 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  597 

be  used  so  as  to  prevent  infection ;  that  is,  so  as  to  prevent  the  pene- 
tration of  the  germ-tubes  of  the  spores.  This  means  actual  coating 
of  the  apples  with  the  germicidal  substance  before  these  germ-tubes 
get  started  on  the  fruit;  and  the  formation  of  cankers  can  be  pre- 
vented by  similar  coating  of  the  limbs.  Again,  if  this  could  be  so 
effectually  done  that  no  fruit  or  limbs  become  infected  one  year, 
control  would  be  accomplished  for  the  next  year  as  well,  save  that 
some  cankers  contain  the  living  fungus  through  more  than  one  year. 
Especially  in  the  earlier  part  of  the  season  a  sharp  out-look  should 
be  kept  up  for  the  first  fruit  infections  and  prompt  removal  made. 
At  this  time  careful  search  should  be  made,  too,  for  cankers  from 
which  the  infection  may  have  been  derived  and  every  thing,  even 
suspicious,  removed. 

Now  all  this  is  practicable  so  far  as  cost  is  concerned.  While 
the  latter  cannot  be  estimated  beforehand,  an  extreme  amount  need 
be  but  the  merest  fraction  of  the  possible  loss  when  nothing  is  done. 
And  the  results  from  proper  procedure  are  assured.  Great  losses 
from  bitter  rot  should  be  charged  up  to  the  orchardist,  not  to  the 
parasitic  fungus,  much  less  to  the  latitude  or  the  weather.  With 
other  things  nearly  equal  it  is,  however,  still  best  to  choose  varieties 
not  so  much  subject  to  the  disease. 


598  BULLETIN  No.  118.  [September, 


DESCRIPTION  OF  PLATES 

Plate  I.  Fig.  I. — Bitter  rot  canker  formed  where  the  limb  was  broken.  Fig. 
2. — Natural  cankers  produced  by  the  bitter  rot  fungus  and  in  which  perithecia 
were  found. 

Plate  II.  Fig.  i. — A  large  artificially  produced  canker  producing  masses  of 
pink  spores.  This  canker  was  divided  and  a  section  removed  and  cultured. 
Grayish  white  mycelium  can  be  seen  growing  from  the  wood  of  the  cross-section. 
Fig.  2. — Pustule  of  bitter  rot  fungus  on  mummified  apple.  Spores  in  the  opening 
above.  (Hasselbring). 

Plate  III.  Fig.  i. — Bitter  rot  on  apples,  pear,  and  green  tomato,  produced  by 
artificial  inoculation.  Fig.  2. — An  artificially  inoculated  apple  showing  well  de- 
veloped concentric  rings  of  bitter  rot  spores. 

Plate  IV.  Fig.  i. — Artificial  canker  producing  many  pustules  of  spores. 
Fig.  2. — An  apple  spur  bearing  a  small  bitter  rot  canker  which  was  induced  to 
produce  bitter  rot  spores.  Fig.  3. — The  end  of  the  stem  of  a  bitter  rot  mummy 
showing  the  marks  of  recent  separation  from  the  limb.  Though  the  apple  was 
taken  from  the  ground  it  gave  forth  spores  when  kept  in  a  warm,  moist  condition. 
This  is  very  unusual.  The  mummy  is  shown  on  Plate  VIII.,  Fig.  2. 

Plate  V.  Fig.  i. — Tendrils  of  bitter  rot  spores  oozing  from  the  infected 
portion  of  an  apple  x  7.  Fig.  2. — Pustules  of  bitter  rot  spores  forming  on  the 
surface  of  a  canker  x  7.  The  most  evident  spore-masses  are  near  the  margin 
above  lower  right. 

Plate  VI.  Fig.  i. — Section  of  a  pustule  magnified  from  a  bitter  rot  canker 
on  limb.  (Hasselbring).  Fig.  2. — Section  of  a  canker  showing  perithecia  of  the 
bitter  rot  fungus  with  asci,  some  of  which  are  escaping. 

Plate  VII.  Fig.  I. — An  out-door  experiment  with  bitter  rot  mummies.  Mum- 
mies were  suspended  on  wires  from  the  limbs  of  a  tree  (see  left-center  of  cut), 
placed  just  above  the  ground,  and.  directly  on  it,  and  left  over  winter.  The 
fungus  died  in  all  cases.  Fig.  2. — A  bitter  rot  canker  formed  where  the  limb 
was  broken. 

Plate  VIII.  Fig.  I. — An  artificial  canker  on  living  apple  limb  showing  con- 
tinued growth  the  second  season  after  inoculation.  Perithecia  of  the  bitter  rot 
fungus  were  found  on  this  canker.  Fig.  2. — Bitter  rot  mummy  bearing  pustules 
of  bitter  rot  spores.  This  mummy  was  taken  from  the  ground  but  apparently  had 
not  been  there  very  long  c.  c.  i1/?. 

Plate  IX.    Fig.  I. — The  old  way  of  fighting  bitter  rot  in  Illinois. 

Plate  X.  Effect  of  copper  sulfate  solutions  on  the  germination  of  bitter  rot 
spores.  Figs.  I  to  7  inclusive  were  germinated  in  4  c.  c.  of  the  solution  while 
Figs.  8  to  15  inclusive  were  germinated  in  %  5  c.  c.  of  the  solution.  The  solu- 
tions were  as  the  following  designated  proportions  of  copper  sulfate  to  water ; 
Figs  I  and  8,  1 : 100,000;  figs.  2  and  9,  1 :200,ooo;  figs.  3  and  10,  1 1400,000;  figs.  4 
and  li,  1:1,000,000;  figs.  5  and  12,  1:2,000,000;  figs.  6  and  13,  1:4,000,000;  figs.  7 
and  14,  1:10,000,000;  fig.  15,  distilled  water.  The  dark  colored  bodies  are 
appressoria. 


1907.]         BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  599 

I 


Fig.  1 


Fig.  2 


600 


BULLETIN  No.  118. 


[September, 

Pi, ATE  II 


UHBB9BBI 


•">, 


Fig.  1  (upper) 


Fig.  2  (lower) 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  601 

PIVATK  III 


' 


Fig.  1  (upper) 


Fig.  2  (lower) 


602 


BULLETIN  No.  118. 


[September, 
PLATE  IV 


Fig.  1 


Fig.  2 


Fig. 


1907.]        BITTER  ROT  OP  APPLES,  BOTANICAL  INVESTIGATIONS.  603 

PIRATE  V 


Fig.  1 


Fig.  2 


604 


BULLETIN  No.  118. 


[September, 


Fig.  1 


VI 


Fig.  2 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.          605 

Pr.ATE  VII 


Fig.  1 


606 


BULLETIN  No.  118. 


Fig.  1 


[September, 
PLATE  VIII 


Fig.  2 


1907.]        BITTER  ROT  OF  APPLES,  BOTANICAL  INVESTIGATIONS.  607 

IX 


608 


BULLETIN  No.  118. 


[September,  1907 
PLATE  X 


1907.} 


AUTHOR  INDEX 


609 


AUTHOR  INDEX 


Blair,  Joseph  C.,  Bitter  rot  of 
apples,  horticultural  inves- 
tigations, Bull.  117 483-551 

Burrill,  T.  J.,  Bitter  rot  of  ap- 
ples, botanical  investiga- 
tions, Bull.  118 553-608 

Crandall,  Charles  S.,  Spraying 
apples,  Bull.  106 206-42 

Dietrich,  William,  Location, 
construction  and  operation 
of  hog-houses,  Bull.  109  ... 
287-302 

Forbes,  S.  A.,  Comparative  ex- 
periments with  various  in- 
secticides for  the  San  Jose 

scale,  Bull.  107 243-61 

Cottony  maple  scale  in  Illi- 
nois, Bull.  112 343-60 

Field  experiments  and  obser- 
vations on  insects  injurious 
to  Indian  corn,  Bull.  104. . . 

94-152 

On  the  life  history,  habits  and 
economic  relations  of  the 
white-grubs  and  m  a  y  - 

beetles,  Bull.  116 447-80 

Spraying  apples  for  the  plum 
curculio,  Bull.  108 265-86 


Fraser,  W.  J.,  Construction  of 
silos,  Bull.  102. 1-41 

Good,  Edwin  S.,  Storage  barn, 
sheds,  feed  lots  and  other 
equipment  for  feeding  ex- 
perimental cattle  in  car  load 
lots,  Bull.  110 303-24 

Hopkins,  Cyril  G.  and  Read- 
heimer,  J.  E.,  Soil  improve- 
ment for  the  worn  hill 
lands  of  Illinois,  Bull.  115 
,....431-43 

Hume,  Albert  N.,  and  Center, 
O.    I).,   Shrinkage    of    ear 
corn  in  cribs,  Bull.  113. ... . . 

361-76 

Lloyd,  John  W.,  Farmer's  vege- 
table garden,  Bull.  105 

153-205 

Spraying     for     the     codling 
moth,  Bull.  114 377-429 

Mumford,  Herbert  W., Compari- 
son of  methods  of  preparing 
corn  and  clover  hay  for  fat- 
tening steers,  Bull.  103. . . 

43-95 

Maintenance  rations  for  beef 

breeding  cows,  Bull.  Ill 

.  .325-42 


1907.] 


INDEX 


611 


INDEX 


The  headings  in  capitals  are  the  subjects  of  entire  bulletins 


PAGE 

Alfalfa  on  worn  hill  lands 440 

Ants'  nests  and  the  corn  root- 
aphis 102-23 

Aphis  Cucumeris 163 

Maidiradicis 102-23 

Aphis,  woolly,  and  the  gasoline 
blast  lamp 145 

Apple  scab.... 216-17,  225-27,  230-31 

APPLES,  BITTER  ROT  OF, 
BOTANICAL  INVESTI- 
GATIONS   553-608 

HORTICULTU  RA  L       I  N  - 

VESTIGATIONS 481-551 

spraying  for  the  codling  moth 

377-429 

FOR     THE     PLUM     CUR- 

CULIO 263-86 

RELATIVE  MERITS  OF 
LIQUID  AND  DUST  AP- 
PLICATIONS  206-42 

Arctian  caterpillar  and  gaso- 
line blast  lamp 145 

Arsenical  poisons,  for  curculio 

266-81 

for  spraying  apples 208-42 

See  also  paris  green. 

BARNS,  SHEDS,  FEED  LOTS 
AND  OTHER  EQUIP- 
MENT FOR  FEEDING 
EXPERIMENTAL 
CATTLE  IN  CAR-LOAD 
LOTS 303-24 

Barrier  experiment  for  pro- 
tection of  corn  against 
chinch-bugs 124-34 

Beef  cattle,  experimental  plant 
for  feeding  at  Illinois  ex- 
periment station 303-24 

Beetles 163,  174-75,  184,  190 

See  also  white-grubs. 

Bill-bugs 95-101 


PAGE 

BITTER  ROT  OF  APPLES, 
BOTANICAL  INVESTI- 
GATIONS   552-608 

dissemination  of 572-94 

HORTICULTURAL    IN- 
VESTIGATIONS  483-551 

weather  conditions  affecting 

533-41 

Black  rot 582-83 

Blackbirds  as  enemies  of  white- 
grubs  and  may-beetles. .  .468-69 
Boll-weevil,    see    cotton    boll- 
weevil. 

Bone  meal  in  soil  treatment. . .  442 
Bordeaux   mixture,    use   of  in 

spraying  apples 209- 

42,  377-429,  484-551,  565-72,  585 

in  vegetable  garden 

163,  174-75,  184,  190 

Bordeaux  nozzle 383 

Bowker's  tree  soap 258 

Breeding  cows,  rations  for. .  .325-42 

Brick,  in  silo  construction 35-36 

Cabbage-worms 163,  175 

"Calcothion"  247,  256-57 

California  wash   for  San  Jose 

scale 247-57 

Cankers,  see  bitter  rot;  limb 
cankers. 

Chilocurus  Bivulnerus 358 

Chinch-bug ......  124-52 

and  gasoline  blast  lamp. .  146-50 
Clover    hay     in    feed    of    beef 

breeding    cows 327-38 

in  feed  of  fattening  steers ..  43-82 
in  soil  treatment. .  .431-32,  439-40 
Coal-tar  line  as  barrier  to  in- 
sects injurious  to  corn. .  .131-33 

Coccophayus  lecanii 357 

Codling  moth,  spraying  for 

218-19,  231-32,  377^29 

"Con  Sol"..  247,256-57 


612 


INDEX 


[September, 


PAGE 

Concrete,  use  of  in  construc- 
tion of  silos 32-35 

CORN  AND  CLOVER  HAY,. 
CO  M  P  A  R I  SON  OF 
METHODS  OF  PREPAR- 
ING FOR  FATTENING 

STEERS 43-93 

and  cob  meal 64-65 

cribs  362,  309 

FIELD  EXPERIMENTS  AND 
OBSERVATIONS  ON  IN- 
SECTS INJURIOUS  TO 

95-152 

prices  of,  fall  and  spring 361 

shrinkage  of,  in  cribs 361-76 

stover    in    rations    of    beef 

breeding  cows. 327-42 

Cotton    boll-weevil    and    the 

gasoline  blast  lamp 143 

COTTONY    MAPLE    SCALE 

IN  ILLINOIS 343-60 

Cow-peas  in  soil  treatment 

432-34,  440 

Crambus , 145 

Cribs,  for  corn 309,  362 

Crop  rotations  for  soil  treat- 
ment  439 

Crows  as  enemies  of  white- 
grubs  and  may-beetles. .  .468-69 

Cucumber  beetle 163,  174-75 

Curculio,  apple 219,  231-32 

PLUM-CURCULIO,  SPRAY- 
ING APPLES  FOR 263-86 

Cyclocephala 449 

Dalbey  field,  study  of  bill-bug 

in 95-101 

Dust  spray ,..207-24 

Dusty  furrow  as  barrier  to  in- 
sects injurious  to  corn. .  .130-31 
Ear  corn,  shrinkage  of  in  cribs 

361-76 

Engine   house  for  beef  cattle 

experimental  plant 309 

Epicauta  vittata 163-64 

Farrowing  pens .293-94 

Feed  bunks 307 

Jots 305-06 

mangers 305 

racks 46 


Feeds,  efficiency  of 80-81 

for  fattening  steers 43-93 

quality  and  cost  of 48-49 

storage  for 304-05 

See  also  ration. 

Fertilizers,  see  soil  treatment. 

Finnegan  experiment  for  root- 
aphis  113-17 

Flea-beetle 163,  175 

Fruit  blotch 217-18,  227 

Frutolin 257 

Fungi,  see  cankers;  bitter 
rot;  mildew;  black  rot. 

Galesburg,  111.,  experiments  for 
root-aphis 103-05 

Garden  soil,  preparation  for 
planting 161 

Garden,  see  also  vegetable 
garden. 

Gasoline  blast  lamp  as  insecti- 
cide..  137-52 

Gloeosporium  fructiye n u m 
Herk.,  see  Glomerella  mjo- 
maculans. 

Glomerella  rufomaculans 557-608 

Gluten  meal  for  feeding  steers 
45-46,  48-71 

Griggsville  experiments  i  n 
spraying  for  codling  moth 
422-27 

Grub-wasp 469 

Grubs,  see  white-grubs. 

Harlequin  cabbage-bug  and  the 
gasoline  blast  torch 142-43 

Harvel  experiments  for  root- 
aphis  105-07 

Hill  lands  of  Illinois,  improve- 
ment of  soil  of 431-43 

Hinman  experiment  for  root- 
aphis 109-13 

HOG-HOUSES,  LOCATION, 
CONSTRUCTION  AND 
OPERATION  OF 287-302 

ITyperaspis  binotata 358 

Insecticides,  fluid 134-37 

for  cottony  maple  scale  . .  .349-55 
for  San  Jose  scale.  .243-61,  257-60 

cost  of _ 258-60 

in  corn 126-52 

in  orchards.207-240,  243-61,  265-86 


1907.] 


INDEX 


613 


in  vegetable  gardens 

163-64. 174-75,  184,  190 

See  also  names  of  different 
insecticides. 

Insects,  dissemination  of  fruit 

diseases  by  574-75 

See  also  names  of  species. 

June-bugs,  see  may-beetles. 

Kerosene  mixtures  as  insecti- 
cides  126-27,  134-36,  243 

for  cottony  maple  scale 349-55 

LachiWHterna   447-80 

Lady-bug 358 

Lasius  Alienus 108-19 

Legume  crops  in  soil  treatment 

431-440 

Limb  cankers 562-72,  581 

Lime  and  sulphur   washes  for 

San  Jose  scale. 246-57 

in  soil  treatment 431-43 

Linseed  cake  in  feed  for  fat- 
tening steers 45-46,  48-71 

MAINTENANCE  RATION 
FOR  BEEF  BREEDING 
COWS 325-42 

Mangers 305,  307-08 

Maple  scale,  see  cottony 
maple  scale. 

May-beetles,  see  white-grubs. 

Meadow  moths  and  gasoline 
blast  lamp 145 

Melon  louse '. . .  163 

Mexican  boll  weevil,  see  cot- 
ton boll  weevil. 

Mildew  and  gasoline  blast  lamp 
145-46 

Neutral  zone  in  spray  ing  experi- 
ments   :281-86 

Nitrogen  in  soil  treatment. .  .431-39 

Nitrogenous  concentrates  in 
cattle  feeding 44,  48-84 

Oat  straw  in  rations  of  beef 
breeding  cows 327-38 

Oats  and  the  root-aphis.  114-18,  122 
soil  treatment  for , 438 

Oil  meal,  see  linseed  cake. 

Oregon  wash  for  canker 572 

for  San  Jose  scale  247-57 

Paris  green  as  insecticide   in 

orchard 208- 

24,  266-81,    377-429,    513,  525-29 


in  vegetable  garden 

163,174,  184,  190 

injury  to  apples  from 405 

Paving  of  feed  lots 306 

Pear-burner 143 

Pigs  as  enemies  of  grubs 478-79 

following  steers. . ... .  .46,  58-61,  81 

Phosphorus   in  soil  treatment 

431-41 

PLUM-CURCULIO,  SPRAY- 
ING APPLES  FOR 263-86 

Poison  tests  of  sprayed  apples 

279-81 

Potassium  in  soil  treatment. 431-41 

Pressure  on  walls  of  silo 2 

Profits  from  fattening  steers. 67-71 
Rations  for  beef  breeding  cows 

...325-42 

for  fattening  steers 50-51,  81 

Rock  phosphate  in  soil  treat- 
ment    442 

Root  aphis 102-23 

Rotation  of  crops  in  soil  treat- 
ment  439 

Roughage  in  cattle  feed. 44-45, 48-82 
San  Jose  scale  and  the  gasoline 

blast  lamp 140-42 

COMPARATIVE  EXPERI- 
MENTS WITH  VARIOUS 
INSECTICIDES  FOR.. .243-61 

Scalecide 257 

Seeds,  vegetable 198-200 

Sheds  for  beef  cattle 305-09 

Shock  corn  in  rations  of  beef 

breeding  cows 327-38 

Short  horn  feeding  steers 44-45 

SHRINKAGE  OF  EAR  CORN 

IN  CRIBS 361-76 

Sibley    experiments     with 

shrinkage  of  ear  corn  —  362-71 
Silage    in     feed    of    fattening 

steers 45-82 

in   rations   of  beef  breeding 

cows 327-42 

packing  of ...      1 

SILOS  CONSTRUCTION  OF. 

1-41 

Smartweed  as  food  of  root- 
aphis 108,  110,  115-16,  119 

Soap  solution  for  San  Jose  scale 

..257-58 


614 


INDEX 


[/September, 


PAGB 

SOIL   IMPROVEMENT  FOR 
THE     WORN     HILL 
LANDS  OF  ILLINOIS. 431-43 
Soy  beans  in  soil  treatment —  440 

Sphaeropsis  malorum 583 

Sphenophorus 95-101 

Spraying  apples  for  bitter  rot 

541-48 

FOR  CODLING  MOTH.  .377-429 
FOR  PLUM  CURCULIO.  .265-86 

for  San  Jose  scale 243-61 

RELATIVE  MERITS  OF 
LIQUID  AND  DUST  AP- 
PLICATIONS   206-42 

Stave  silos 37-41 

Steers,  fattening. . .   43-93 

Stone,  use  of  in  construction  of 

silos 36-37 

Storage  barns 304-05 

Straw,  in  cattle  feeding 44 

See  also  oat  straw. 
Tak-a-nap  soap   for   San  Jose 

scale 258 

Thompson    field    experiments 

for  root-aphis 117-18 

Timothy   bill-bug,   injuries  to 

corn  by . .   .       101 

hay  in  cattle  feeding 44 

plant,  injuries  to,  by  bill-bug 

96-97 

Tiphia  inornata 448,  469-72 

Tomatoes . .  .164-65,  175,  184 

VEGETABLE   GARDEN, 

FARMER'S 153-205 

cultivation  of 174,  183-84,  190 


labor  in 158,  176,  184-86,  192 

planting  of.162, 170, 182-83,  189-90 

Vegetables,  harvesting  of 

167-68,  177-78,  186, 193 

late  crops  of 153,  175-76 

Vermorel  nozzles. . . 383-85,  403 

Vienna  experimental  field  for 

soil  improvement .432-36 

Water  supply   for  beef  cattle 

experimental  plant., 307-08 

Web-worms  and  gasoline  blast- 
lamp 145 

Whale  oil   soap  as  insecticide 

for  chinch-bug 137 

for  cottony  maple  scale 353 

for  San  Jose  scale 257-58 

Wheat,  soil  treatment  for 

437,440-41 

WHITE-GRUBS  AND  MAY- 
BEETLES,  LIFE 
HISTORY,  HABITS  AND 
ECONOMIC  RELATIONS  • 

OF 447-80 

enemies  of 468-75 

food  and  feeding  habits — 454-57 

hibernation  of 467 

injuries  to  crops  by 477-78 

migrations  of 457-62 

prevention  and  remedy...  478-80 

reproduction  of 462-66 

soil,  relation  to  476 

Winesap  apple  and  the  codling 

moth 413 

Woolly  bears,  see  arctian 
caterpillars. 


T  i^i^aHlfS  aiLVT^ 


